discipline3 (and some parallels.. metal mickey??) work the other way.. eg. having 5 different length delay taps on the signal and crossfading between them at the output. you're describing putting the selection at the input to the delay taps.
i also think this would sound quite nice, especially with slow modulation of feedback, eg. some taps would have a bit of dub feedback colouration then cut back.
have you tried using a modular environment? (i haven't tried eXT2's mod. environ yet,) i used eXT1.4 to do things like this.. it took some intermediary effects plugs i pieced together in synthedit that had two outputs and would fade the signal between them. chains of signal splitters could be created leading to several delays, reverbs, granular effects.
so eg. to accomplish the delay scenario, a path randomiser could be applied to a few delay instances, with MIDI lfo plugs targeting the regen params.
actually (here's me having only recently woken up) this has a drawback bcs afaict multiple outputs only seemed to function as mono (despite the 'stereo pair' compile option..) which leads to a mess bcs a bunch of extra vst are then required to pan and recombine signals into stereo..
otherwise, this would do better bcs a dedicated effect would wear itself out after a couple of applications (albeit with ambient, those applications may be 80 minutes in length..) having to code an intelligently selecting randomised pitch shifter would be a lot of work to achieve the same end.
i'll have a mess with the multiple outs thingy and see if i can get it to pair correctly. if not.. 8 stereo delays, resonant filter on each.. wouldn't take too long to code. i could throw a few ck pitchshifter modules in and taps could be assigned to them.. if you don't mind a crap gui

i've only coded the crudest pitch shifting algo.
then again, maybe waiting would be best

i've built an fft but haven't "done" anything with it yet..
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