My ideal one should give an interface like nanoloop 2.
Has multiple system built it : gb/sms/genesis/opl2/opl3/other, advanced sample editor.
Give the same kind of power that a Elektron md, monomachine, octatrack and analog 4 give.
I will maybe take ten years more to build it, but this will be my ideal advanced step sequencer.
I may have too much hope, but maybe one day I will be able to create this.