Just dropping a comment in this thread as well, as there are different people here than in the thread in Rackmount.

I’ve built one with tone control in the feedback loop, and have just made one with a parametric band in the feedback loop.

They are available here – https://godlike.com.au/index.php?id=420

I’m interested in collaborations with anyone to build new stuff.  I’m going to have a look to see if I can replace the delay modules in this algorithm with mod delay, micro delay or ramp delay to make smooth delay time changes, as some people seem to want this functionality. Probably more for the guitar folks than the synth folks, but it should also smooth out glitches when clocked delays are changed as well.