This actually makes quite a bit of sense, and I'm a little surprised that no one's tinkered with no-input feedback paths all that much in Eurorack.
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. Add some modulation, a bit of the typical Eurorack voodoo, stick it all in a Behringer cab, and I came up with:
Pretty cool...the left end is the modulation section, uses a Maths, Quadrax and eight free-run LFOs, plus a few mixing/modification modules to make that do a ton of interactive crossmodulation, plus output some VERY wild curves. You get six VCAs (switchable curve) after that for modulation and audio amplitude control as needed. The "beefy" part is in the center, where you'll find an 8 x 4 matrix mixer plus a pair of Pittsburgh Delay Networks, and there's also a touchpad-controlled switch for either audio or modulation. The right end (audio processing/output) contains eight VCFs, a really useful output processor (the T-racks...I have the standalone version, and it's VERY feedback-friendly), plus your submix from the four outputs of the matrix (you'd split these...and for that, I also added four buffered mults to make sure the audio levels stay up when splitting, if necessary). Then there's an Isolator for your isolated stereo outs plus your master output level.
Now that's a nice start-point...or if you like, a finished solution.