I had experimented with plugin development a few years ago, but I only recently got the time to actively pursue it, and I just completed my first "fully finished" plugin.
This plugin is admittedly a bit on the simpler side, but I'm hoping to pursue more ambitious stuff eventually. Plus, though this is simple, I'm not sure there's anything else quite like it; it's a comb filter where the delay taps smoothly interpolate in the time domain, and this leads to pitch/time bending of each delay tap individually. I have some audio examples here https://notwoowoo.github.io/plugins/
The source code is also available on GitHub https://github.com/NotWoowoo/honey-comb
I wanted to avoid the bloat that comes with popular plugin frameworks like JUCE and IPlug, which I've found to be overly complex with a lot of overhead. My past experiences with these led me to try a lighter approach: a very light library called CPLUG (https://github.com/Tremus/CPLUG), glfw (https://github.com/glfw/glfw) for window management, and nanovg (https://github.com/memononen/nanovg) for graphics.
I'm really curious to hear thoughts from musicians, plugin devs, or other DSP-related) developers. I've been working in this space in relative isolation, and I'm sure there's a lot for others to shed light on.