My advice would be to make something genuinely different - not just a compilation of other peoples designs.
If its remotely close to another module design, then scrap it. Please don’t make a filter or drum module
The other thing i’d say is it must be skiff and hp friendly. hp wise - no more than a Maths 20hp - ideally 10 hp or less. If its a utility module 4hp is ideal. If its more than 20hp then it better be amazing and completely unique.
Stiff knobs, not wobbly knobs. No matter what people say about how great wobbly knobs are to the actual function it doesn’t matter. Its about the user experience and wobbly knobs subconsciously doesn’t make you feel good. I am saying this as a Harvestman and Buchla user that both user wobbly knobs. You will alienate buyers with wobbly knobs. No fancy bold graphics / no colour - think Greyscale not Snazzy Effects. Sorry, no offence Papernoise, but in my opinion, its a no to cartoon graphics. It looks like a kids toy, again you will alienate your users - i’m looking at the likes of Endorphin here. The best example i’ve seen with nice graphics and no colour would be the Manniquins stuff which is quite arty, its minimal, but not in your face. If i was making a module i’d just let greyscale design the visuals. They are boring, they are plain, they are clear, concise and whats most important is no one complains about them. It saves people spending extra money changing knobs / faceplates in the long run. Also no colour, use silver faceplates. The only manufacturers that can get away with that in my opinion are Metasonix and Cwejman.
Unique knobs can be handy to make it stand out - not the cheapo nasty ones on the PEG but solid ones like on the DLD.
I live in a humid environment and my other pet peeve is the materials for some components - like screws, standoffs, washers and metal shafts in encoders (i prefer plastic) in knobs being open to corrosion. Its easy for me know which manufacturers scrimp on this after a few years in my case.
Benchmark modules that have passed the test of time component wise with zero corrosion would be Livewire, Cwejman, Synthesis Technology, Mannequins. I know why their stuff is more expensive!