After reading your question and all of the answers here I still don’t understand what exactly you want or are missing with the existing gear and apps available, and what makes Elektron sequencers and alike awkward when used in different time signatures.
The only real limitation with the Elektron style sequencer that I’m aware of would be polyrhythms aside from 3:4 type of stuff. You can remedy this to a great degree by using polymetric patterns combined with the 3/4 seq speed and individual track lengths.
Some ipad apps are pretty good for a truly non 4/4 approach as the GUI can be adapted to any divisions you want but in hardware it would be pretty difficult and complicated if not unrealistic.