A few things I need to figure out:
(Please suggest solutions!)
- Which 1.5u Delete key to use.
- Whether it's worth including a second 2.25u Shift key.
- Whether the 1.75u Function key is worthwhile.
- Whether two 6U spacebars is worth it.
- How many ISO keys to include in the base - I'm trying to keep the cost down.
I'd be down for this.
Here is my take on some of the items you need to figure out.
1. 1.5u Delete: make it a <---- arrow icon backspace. I think it looks neatest from my experience owning multiple sets (see GMK Taro). Please do not use the < [X] backspace icon.
2. I think including a second 2.25u Shift key is useful for Clueboard and Leopold 660M users, etcetera. There is also use for the Shift key for other reasons, such as split spacebar, etc.
3. I don't think a 1.75u Function key is worthwhile, but I think you have the ultimate say on whether it should be included. I also wanted to suggest adding a stepped 1.75u R3 Control key. A lot of people use the Control key in that position, and personally, I
always prefer the look of a stepped key in that position than a non-stepped one. Other sets have included Stepped Control, and it's been nice (see kekkon's GMK Dolch). If you won't include it, I'll live with it, but I'd recommend it

4. I think the simplest form of ISO would be best -- that is, ISO enter, the two keys that go in the R3 row, short 1.25u Shift, R4 pipe key. Optionally you can include ISO-UK keys, which are the 1, 2, and 3 keys on the number row.
5. Other suggestions that I'd like to make.
a) Inclusion of 1u R4 00 key for splitting the 0 key of the numpad section.
b) Alternate homing key for the 5 in the numpad. I prefer a scoop for all my homing keys. I'd personally recommend having bar for one key, and scoop for the alternate.
c) R5 bottom row? With GMK Carbon R2 having been made successfully, we now have molds for R5 support for 1.25u mods as well as 1.5u mods. It's great. I think we should take advantage of it.
d) You are missing a 1.5u modifier colored Pipe key.