It would be great if a quality karting mod came out for rfactor! However, my understanding is that the rfactor physics engine does not cope with the low mass of karts. Consequently, I believe karting mods so far have had to make the karts artificially much heavier than real life...
In fairness to the kart mods out there, to date, I have only tried an early release of one of them over a year ago (which suffered engine damage within a lap due to overheating).
I've only ever been kart racing once, that was a few years ago in Newquay (Cornwall), where the sense of speed and their amazing grip was a great 2x15 minute experience!