So, monoporpellant (to me, at least) looks like a obvious KSP analogue to hypergolics, not only due to it's use in RCS, lower specific impulse and the real-life monopropellant being usually hydrazine, but also because it was used in a couple of major mods with engines, the source of inspiration for which used hypergolics IRL. Those are, unfortunately, nearly all upper stage engines - but in real life there are rockets using hypergolics on lower stages (Proton as an example, through @Beale transitioned to using LFO even in his RCS, so it's unlikely we'd ever see it in Tantares' Proton). In general, it pains me to see a stock (!) resourse so horribly underused - confined nowadays only to RCS and a couple of small secondary engines. Proton engines have a pretty distinct look and could look great in some cryoengines style mod, but I doubt any major modders would be interested in such developement, as I haven't seen much love for monoprop in KSP community. But that's my thoughts on the subject, that do y'all people think of all this?