There’s a great little tool for this already 
you can do convincing tape stops by resampling and down pitching either in the modulation section or using track fx commands. sometimes it helps to add a LP filter with decreasing cutoff frequency simultaneously. a workaround, to be sure, but usually does the trick
I’m with you on the other stuff! Especially modular synthesis with various engines. wavetable, FM (cross modulation of any source to any other would be ideal), and granular being my top three most desired. this would be a major code rewrite for the cross modulation, at least, so, I’m not holding my breath for any of this stuff. I believe that devs view plugin support as taking care of these needs. which, they do. I just want renoise to do EVERYTHING, lol…