This is mostly me rambling about “wrong” uses for X5R capacitors. People tend to avoid these as the plague, as their capacitance drops A LOT compared to other types.
The smaller the caps, the bigger capacitance drop can be achieved. 1u seems to be the sweet spot to get the biggest voltage drop (at least according to Kemet KSim). 0402 are rather tiny for hand soldering, 0603 should be a good compromise.
However, the max capacitance drop is slightly less than one order of magnitude. As a comparison, LDRs tend to have about two orders of magnitude change, JFETs even more. These however need additional circuitry (LEDs, biasing etc.) while capacitors just need the bias voltage, possibly straight from the LFO (or none additional circuitry at all!).
I might try to do a Phase 90 clone using these caps, as the conversion is theoretically rather simple:
More promising use for these caps would be filters. In these circuits series caps do not seem to work as well (if working means higher distortion from input signal). 1u caps are rather big and would limit to very small resistor sizes. Smaller caps do still work similarly but with lower capacitance drop.
As an example, creating passive “reverse slewing filters” (= highpass filter that limits louder signals instead of lowpass) would be really easy:
There is a VST called Capacitor2 from Airwindows to check out what these kinds of filters would sound like.