Good questions.
How will we know that an input or an output can handle polyphony?
You should assume a module doesn’t unless the module has a “Poly” tag in the Module Browser. If it does, most inputs/outputs will be poly within reason. Obviously, the RUN trigger input of a sequencer will be mono, because it would be ridiculous otherwise, and so on.
will there be a module to combine voices to create a polyphonic patch to use other sources than midi (sequencer module) like 16in 1out?
Yes, this will probably be called VCV Poly Muxer proposed in VCV Poly: ideas for a new standard polyphonic utilities plugin
will there be a module to explode polyphonic patch 1in 16out to make voice stereo panning à la OB-X?
VCV Poly Demuxer
will there be any way to tune each voices separately in the same module, to mimic analog unstability of the components ( fine tune vco, light cut off difference?
Fundamental VCO will do that in its default ANLG mode. I see no need for Fundamental VCF to do that with cutoff frequency since that effect is 100x more subtle than VCO pitch drift. Other than this built-in analog-modeling pitch drift, the only way you can create pitch differences between channels in VCOs is to offset the polyphonic 1V/oct signal yourself.
If I use monophonic cable into a ployphonic cable, please tell me we wont have all the virtual polyphonic engine runing for nothing in the background…?
Do you mean “monophonic cable into a polyphonic input”? There is no such thing as a poly input. The number of channels of an input is always equal to the number of channels of the output on the other end of the cable.
does it mean we can one day hope to chain those mutable stage sequencer?
I don’t see how poly cables has an effect on that feature.