viability of using a fet as a voltage controlled resistor in a HPF

[SoulFetish]

Yes. Look up envelope followers.

haha! so I just looked it up, and turns out my developing idea had already been well a established thing. Good to know I was on the right track anyway...
Okay, so, I'll have to do some more reading and probably some experimentation to figure out some good ways of creating an envelope filter for this.
One of the things I'm curious about is whether I'll get the best results from using signal voltage taken directly at the input, right after the first gain stage, or in a later stage in the preamp.

uneumann, I was asking my boss about those LM13700 or the old CA3080, and I think we actually have some stock of both of those in the shop

[eschertron]

A lot of DIY circuits with the venerable CA3080 were made available in electronotes (Bernie Hutchins) with many of my favorite designs by Craig Anderton. I took a couple electronic music courses in the early 80s just before MIDI became a thing - when analog synthesis was still alive - and built a few VCA/VCF-type circuits around the CA3080.
I have a few chips in my stash. Let me know if you turn up empty-handed, I don't know if they are still available from Mouser, et. al.