Well, obviously, you’ve seen my thread about it 
https://forum.renoise.com/t/adding-monoizer-to-the-gainer-dsp-effect/20016
Just wanted to add that there will always be practical reasons to check the result in mono. Even if you don’t hear Renoise tracks on your mono-radio everyday, you could easily play your songs on your cellphone (which are mostly mono).
By the way, if you’re concerned of making your tracks work with vinyl, I think you should check out otiumFX BassLane instead (put it on your master). This will monoize your song up to a given frequency, f.ex from 300 hz and downwards, which is essential to keep the needle in the vinylgroove. On the other hand, the vinyl-mastering-crew will often take care of this, nevertheless you can still check how it will sound roughly.