First of all, what do we mean by incel? The widespread use of the term is fairly new, but the concept has been around for awhile. Back in the PUA era, when people in the manosphere thought of an "incel" they pictured a guy who didn't know any game, and probably hadn't stylemaxxed yet. Now that men are more game-aware, and lookism has become such a big deal, when people think "incel" they usually picture a guy with a really ugly face (even though a lot of the original PUA gurus were short, bald, ugly dudes; in fact, one of their major selling points was that their training supposedly could get ANY guy laid).
The broadest definition of an incel is that it's anyone who temporarily or permanently can't get laid without raping a girl or paying an escort. Thus, for example, if your wife just had a kid, and you're waiting for her perineum to heal; or if you're stuck in traffic on your way to your girlfriend's house to pin her ankles behind her ears and smash her cervix, you might be a "tempcel" (temporary incel). Some in the incelosphere would object to this, and say that you're only an incel if you're a "truecel," i.e. a guy who under no possible circumstances will ever get laid. I.e., you're a guy who's going to be a KHHV (kissless, hugless, hand-holdingless virgin) for life.
In practice, though, the incelosphere consists mostly of youngcels (teenagers, college students, and others who haven't had a chance yet to betabuxx for some pussy, and perhaps lack favorable logistics), and MGTOWs (guys who got pussy in the past but now are divorced and/or unemployed men with slim to no easily realizable romantic prospects). The number of hideously ugly men in the incelosphere is low, as many who pretended to be such were later revealed to be fakecels, i.e. men larping as extremely ugly men; some of these were actually chadlite-tier, it turned out.
One of the main schisms in the manosphere is between the game-focused and politics-focused manospherians. The game-focused guys just want to stack paper and bang hotties, and regard the politics-focused guys as idle complainers and game-naive incels. The politics-focused guys regard the game-focused guys as hedonists who are just "enjoying the decline" rather than putting in work to save society.
Not all incels are political, though; nor are all political manospherians incel. The incel community split off from the rest of the manosphere because incels wanted a place to discuss their "copes" (i.e. activities they engage in to make the best of their incel lives), and the blackpill (i.e. the hopelessness of their situation) without being judged for not doing more to improve themselves and their game so they could get pussy.
With Roosh essentially becoming a religioncel (i.e. a man who either goes religious because of his celibacy, or celibate because of his religion), the schism has deepened. Probably few RVFers are religious married men, and it's been pointed out that modern marriage is a scam in western countries, so it seems likely that the community will go in a more incel direction.
Meanwhile, the rest of the incelosphere has not held up well against the waves of censorship with which it has been hit. In 2017, r/Incels was banned and the community never totally recovered. Some users went to r/braincels, which along with r/TheRedPill was quarantined in 2018. Others went to Incels.me (now Incels.co), which after the Toronto van attack in 2018 became nationally famous but also had to make concessions to the censors, eliminating violent (e.g. pro-rape and pro-mass killing) rhetoric. In 2019, the moderation at Incels.co became totally abysmal, with many high-quality users getting banned.
Meanwhile, there has been some talk of femcels and incels, which are generally women in their 20s and 30s who have not settled down with a husband and kids yet, but say they would like to. More on that later.
One possible purpose of the incelosphere which seemed promising was that it could be a more radicalized group of men than the rest of the manosphere. This gets back to the schism mentioned above, between big ballers and incels. The "big ballers" are reluctant sometimes to admit their failures; while the "incels" often don't want to admit their successes, lest they be kicked out of the incelosphere for not being incel enough. But there are many men in between KHHV and big baller, who don't really fit in anywhere; e.g. the nearcels who have had some romantic successes, but not any longer.
Meeting in person, or becoming a public figure, could be threatening to both some big ballers, and some incels, due to the threat of (1) having one's claims on the forums be debunked, and (2) getting doxxed. But as long as these communities remain anonymous and online-only, it may be hard to go to the next level of collaboration, organization, etc.