if the number of knobs/control don`t matter,
one could think of the following setup with multiple tap reverb
(be it 3011, 3214, or multiple "discrete" BBDs):
a rotary switch for selecting which tap as a general output (decay),
and one for selecting which tap(-s) to feed back (density).
Probably feeding the shorter taps with more "highs-content",
while feeding back the longer taps through steeper or lower cut-off low-passes.