Hi,
in fact I thought of exactly the same things you mentioned (insert, sequencer, xy control) when I made Synthi.
back then I didn't like the fx insert idea because you can't modulate fx inserts, and the core feature of Synthi is its modularity - every module should be able to be modulated by any other module.
for the sequencer(s), problems would have occurred with a) space, as you mentioned, and b) dsp usage, resp. time to load the device. together with the difficulty whether to choose gate, control, note, or all of them.
ok, the good news is, I found out a solution recently:
it is possible to have as many ins and outs for insert fx as you like!
http://www.cwmodular.org/files/LpFilterStereo.mdl
simplest device but can be loaded as an insertFx and be modulated, by choosing two mod sources for cf and q. (note: to deselect a mod source, choose same mod source again, and its gone).
so, for a future version of Synthi, I could outsource dsp-hungry modSources -like sequencers- to external devices (eg Modular).
problem, as always, is time, but where there's a will there's always a way
