So while I haven't completely finished the first board yet, I'm very happy with the results so far, and unless there's a compelling reason to go back to the ATTINY828 or something similar, I'll be sticking to devices that will sit on the i2c bus.
As for the plate, I've used both 3mm & 1.5mm acrylic to test. The 3mm is nice & rigid, but obviously the switches won't snap into that. 1.5mm is fantastic because the switches snap in easily, however it can be fragile. I have a couple ideas for the case I'm going to try tomorrow that I'll post up.
For the kit, everything SMD will be presoldered for you, the only thing you'll need to solder is switches + LEDs.
On the USB port, I'm sorry, but you'll most likely never see a USB micro on one of my projects. I've had way too many issues with them pulling off, and space isn't at a premium to really require a smaller port.
And regarding the controller, I'd much prefer to design something that's meant to fit what I'm doing, then working around someone else's design. This also has the advantage on the business side for me and on the consumer side for you guys, as a custom controller is cheaper in the mark up then adding something like the Teensy.
What I have in mind at this point is an option for users.
1) Arduino compatible - This version would use a bootloader similar to the Leonardo and behave like an arduino based controller. Obviously there are some set backs and caveats, but this is basically the entry level controller for someone who wants to learn to hack their keyboard.
2) HID device (not Arduino compatible) - This bootloader would allow for the keyboard to work at start up, support nkro (hopefully), and would be for users who either have no interest in hacking their firmware, or are advanced enough to go with the straight C.
These would be the same CPU board based on the ATMEGA32u4, just like the Teensy 2.0. Because of the modular nature of the controller, I have it on my list to look at something ARM based down the road, as the processing speed & ram would make implementing the macro recording and whatnot a fair bit easier. Again, due to the nature of the design this would be an easy upgrade for just about anyone. If the kickstarter goes really well, it just end up as a stretch goal.
Regarding the keystation, I consider that to be the deluxe version, and would definitely be an addition to the base kit. The whole idea was, and will always be, modularity to allow you to customize it to your needs.