After a lot of thought and private discussion with TK., it will be difficult to realise a new SEQ front panel in the given form. The initial concept started very simple and has morphed into something much bigger.
The main problem is the new hardware options will significantly change the handling and software. All new ideas sound great, but someone has to code them, and support bug fixes/new feature requests. I am unable to do so, and TK. has indicated he won't have time. So we have a choice: either fork the current software with new options (i.e. SEQ v5), or work within the constraints with some hardware improvements.
Assuming nobody wants to step up to take on the coding, a "take one step back" approach could have a 16*3 Matias matrix, with "duo" LEDs for the GP buttons, single colour otherwise, and jog wheel + group/track/layer buttons (+ other suggestions?).
16*3 keeps with the current, adding 4 buttons which are relegendable anyway. So you can give the F1/2/3 buttons dedicated labels too. The keyswitches are nicer, and the panel is simpler. I would need to check, but it's likely the front PCB would be amenable to panel mounting = much simpler case/mechanical design.
I'm sorry to those expecting a 16*4 RGBLM for Christmas...