As you've indicated that this will be a CM Storm product, I'd like to specifically address gaming on an ergonomic keyboard, as that's something that ergo boards historically haven't taken into consideration in their design (and many do rather badly without significant customization). Mechanical ergonomic keyboards are rare enough as it is. Mechanical ergonomic keyboards designed with gaming in mind are pretty much nonexistent. It's not as if gamers never suffer from RSI or desire more comfortable typing--this particular market niche just doesn't cater to them. I'd very much like to see a gaming oriented mechanical ergo board done right. If you guys are going for it, I wish you all the best!
I'm an avid gamer. I've used a variety of ergonomic keyboards over the last couple of decades, primarily the various incarnations of the Microsoft Natural line. I really liked some of the early iterations, though I never really warmed up to the Natural Ergonomic 4000 or later editions (the slope never quite fit my pinkies properly). I've played with a handful of others from Logitech and the like. I've been using a
Truly Ergonomic Computer Keyboard as my primary keyboard at home for the past year. I recently acquired a second one and hacked the firmware to help create an ideal hotkey setup for playing all three races in StarCraft 2: Heart of the Swarm with virtually no need for hand movement. With a bit (okay, a lot) of customization, the TECK is now the closest thing to a perfect gaming keyboard for me, but it took a lot of work to get there.
As for switch type...Switch type is not really a comfort issue, per se. Or at least, there's no general answer as to which is most "comfortable" because that depends on personal preference and how you're using the keyboard. I'm currently a fan of Cherry MX Browns. The tactile feedback is nice for games with a lot of high APM switching across a wide set of keys, and I'm not the type of gamer who enjoys parading loud clicking in front of my stream viewers.
I note that many of CM Storm's current keyboard offerings are available in multiple variants with different switches. If it's at all practical to do so, providing a choice is really the best option. You guys probably know your way around these issues already. Just rest assured that there's nothing particularly special about ergonomic keyboards that affects switch preference differently from standard mechanical keyboards.
O-rings are nice, and definitely a comfort bonus, thought I'd worry about adding too many extras to a mechanical ergo keyboard, which is likely to be quite pricey as is (extant offerings of this type are hard to find for under $200). Offer them as a DIY accessory, perhaps, unless you've already crossed into the range where the target demographic is less price sensitive.
As for backlighting...Backlighting is almost never "necessary", at least not with respect to ergonomic considerations. Ergo keyboard buyers are rarely hunt and peck typists, so lighting effects would be purely for show. Not that that's a bad thing, if it can be implemented cost efficiently, but it's not much more than a gimmick for style points. If you're forking out for an ergo keyboard, comfort takes precedence.
As for layout...The thing that's bad about regular keyboards, and the reason that people buy ergo boards instead, is that the standard design positions your wrists and fingers at angles that are actually rather unnatural. So, in order to make a keyboard ergonomic, you need to design it to encourage more comfortable hand positioning.
But that's not necessarily good for gaming.
Many games assume by default that you will have 6 columns of hotkeys accessible to your left hand (assuming a right hand on the mouse). At the very least, they'll make use of the 1-6 keys. I've seen a number of RPGs and strategy games that also place important hotkeys on Y and/or H, though that's somewhat less common. Such hotkey setups are the bane of split keyboard users, because the "natural" place to split the keyboard puts only five columns of letters/numbers at your disposal. Split keyboards that retain much of the standard staggered layout (such as the MS Ergonomic line) usually at least have the 6 key on the left side.
Most FPS and MOBA style games (which place most important commands in the four home columns) are okay on a split keyboard. Even significantly more comfortable that on a standard one. However, MMORPG and RTS games can be borderline unplayable at higher levels without significant hotkey customization. The standard hotkeys in a game like StarCraft 2, for instance, are all over the keyboard and a nightmare to use with a split layout. It becomes workable if you switch to the command card "grid" layout, but you still lose half your control groups, and important commands are rarely on the home row. And in MMOs, you typically have so many abilities at your disposal that you need all the hotkeys you can get.
A Logitech style wave is perhaps okay for a "safer" foray into the ergonomic keyboard market, as it provides a bit of extra comfort without having to change your typing style, but honestly I think you may as well go all the way and design a proper split keyboard. I find that in attempting to compromise with a happy medium, the wave delivers the worst of both worlds. The angle is not sufficiently aggressive to make it more comfortable than a proper split design, but it's curved just enough that reaching over to use the wrong half of the keyboard while mousing is not very comfortable.
I suspect you'll find a lot of the posters here biased towards split keyboards--probably with matrix layouts to boot. Once you're used to it, that's by far the most ergonomic and comfortable solution. My experience with the TECK leads me to believe that a simple wave distribution of the columns in a matrix layout can largely eliminate the need for the keyboard itself to be curved (assuming an otherwise comfortable split layout). Not to mention that a keyboard with flat PCBs is much cheaper to produce and more comfortable when you need to peck at keys on the wrong half. But I cheerfully acknowledge that I'm no longer a "mainstream" keyboard consumer, and matrix layouts are admittedly a kinda niche thing with a significant learning curve. They really penalize any bad typing habits you may have developed. It's very much worth the effort, though.
Some other comments...The wrist rest often makes or breaks an ergonomic keyboard. Really, it's all about keeping the wrists comfy. I like the semi-cushioned ones, though those should be either removable or shaped in such a way as to enable easy cleaning, as those materials are a magnet for gunk.
Early versions of the MS Natural keyboards were designed with the option to raise at the front (under the wrist rest) instead of the back. Honestly, I found that so much more comfortable than trying to angle the keyboard down from the back that I wonder why nobody does it anymore.
Ergonomic keyboards should be designed with a mind towards reducing hand movement. Keep things close together, don't park the F-key row out in the middle of nowhere, and so on.
Well-positioned, well-shaped thumb buttons are awesome.
The central gap between the halves of split keyboards (or the inner edge of separated boards) is a great place to put extra programmable keys. You normally won't hit them by accident unless you've developed a lot of bad typing habits, but they're at your fingertips when you need them. I've now become so used to the middle keys on my TECK that I wonder how I ever got along without them, and they go a long way towards supplementing the normally key-starved split layout in games.
Hope that helps some. Good luck with your project!