Great feedback - keep it coming

I'd like to get a sense of how many people would be interested in a board. Th XEF232 is expensive and I estimate a BOM for this board to be around $35-$50 depending on parts purchasing volumes. So maybe $100 for the board to cover R&D, BOM, assembly/fabrication, etc.
I'm still planning on a daughter board with ADC/DAC and analog circuitry for guitar applications. That board wouldn't be very expensive. Or folks could interface to their own analog board via I2S.
Yep it's a bit of a beast and offers way more DSP than many folks might need at the start - just one core can do multiple speaker crossovers or a 31-band EQ. Impulse responses takes a lot of DSP - about one core for every 12.5 msec (at 48 kHz). Overdrive effects, done properly with up/down sampling, look-up tables with interpolation, anti-aliasing filtering, and tone shaping takes about one core per gain stage.
If there was a community site that hosted effects that could downloaded then folks could chain many effects and perhaps then then the DSP power could be utilized (e.g. 3xOverdrive-->multi-voice chorus-->cab sim). I can get that going with sample/starter effects and a command-line utility to load the effects via USB MIDI. You could use MIDI to select different chains, change parameters of effects in the chain, set how USB audio is used (to record guitar, mix effects output with computer audio, etc).
I don't have the time for a nice multi-platform GUI application (like an effects builder and/or configurator). But others could make one since the DSP board is just a USB MIDI device. Another idea is to have a Raspberry Pi act as a USB MIDI host and send MIDI to control effects parameters based on other inputs (like knobs, touch screens, etc).