maybe I have one thing to say.
you seem to be enthusiastic about dsp stuff, but also you seem to lack deeper experience with the matter that would be needed to name things so deep in the implementation side.
For example it could very well be, that the renoise analog filter already has some saturation stage in its "feedback path". Else it would be rather daring to present it with a reso tuning that goes into auto oscillation. Dunno about the drive characteristics, they are rather plain and sharp, that's right, not as quirky and warm sounding as other va filters on the market. But then again maybe that's mostly noise generators missing in the algo and the simulations being simplified a lot.
And you cannot just plug some formula into a filter like you would wire up things in a modular synth. There's quite some engineering and balancing involved to make it not blow up speakers on regular basis.
And a FIR filter has no feedback in the algorithm by definition. I also doubt the Renoise EQ uses FIR Filters, those are more probably runge kutta or derived biquads or similar IIR filters. Yes, one could code the appropriate VA Filters with nice coloring and drive characteristics, stack them to make a dope EQ out of it - like on the market as plugin, if it sounds real good, it would cost more than renoise altogether and eat cpu like 10 of renoise's native EQs.
I wouldn't hold my breath for renoise becomming state of the art natuve plugins overnight and by forum demand. Don't underestimate the amount of engineering that has to be put into such devices. I believe the native plugins are rather though as simple and efficient bread and butter stuff that is light to the cpu. Use $$$ plugins if you want the refined sound.
Oh, and a soft clipper for mastering - in projects where I restrict myself to only native devices and don't want to use the soft clipping that is fixed to the end of the master chain, I use the distortion device, in shape mode at 6% drive will just chop everything to level without overdriving hard. You need to pre/post gain it properly with other plugins like the mixers or gainer to control the threshold. But it works, not silky sounding, it will eat the peaks though.