Thanks everyone for the detailed answers.
This system is very interesting! Since I already have a somewhat developed "sampling" section (W/, Nebulae and other stuff) I think it will be very cool to integrate it with something similar to what you describe, Lugia.
As for the matrix mixers, I'd be genuinely curious to know exactly what the 138n cannot do that the lion can. The price gap is quite wide, so I'll take some time to decide. DivKid's video is very comprehensive, but I also found a lesser known video of someone playing with a 138n and feedback. (What would happen if I played them with Landscape AllFlesh cables? That would probably be quite something.)
If you go back to one of the pioneers in this, namely David Lee Myers (ie: Arcane Device), his systems were largely built around matrix mixers tandemmed with delay lines and some other filters and timbral modifiers. This should be VERY easy to implement in Eurorack.
I actually didn't know Arcane Device. Listening now. WOW...