X-Men

Yeah.  Also, the X-Men fans were a huge part of the most devoted IMDB users.

It looks more likely that X-Force will be rated-R now.

Deadpool will be a part of X-Force, though. Also there is a possibility that X-23 could join as well, since she is a member of the team in the comics. So how can you not make X-Force rated-R? Besides, the whole concept of X-Force is that they take on more extreme and violent methods to take down their enemies that the X-Men would never do. 

Interesting though that the likely R-rated successes have different sub-genres. Deadpool is subversive and comedic and found its own market. Logan is expected to be dramatic, violent, and more focused in scope ( compared with team movies) and will likely rekindle the fascination with the Wolverine character.  Similarly, both movies explored characters.  How will a team-up of these two characters work, if what fans want of a team-up happens.

Or does this signal that fans want more solo spinoffs?  Or a combination of solos and team movies?

What about the unusual and effective marketing strategies used for Deadpool and Logan? Deadpool was unabashed in poking fun at everything. That interview of Ryan Reynolds crashing in on a promo of Hugh in Eddie the Eagle was very funny... Logan did not use the traditional way of promoting XMen movies. The first trailer of Logan alone changed the way people were anticipating an XMen movie. According to FOX insiders, as reported by The Hollywood Reporter, Logan drew the highest number of views of a trailer in the entire franchise. It even encouraged imitation by other forthcoming film projects.

Deadpool has already proved the worth of its marketing strategy backed of course by the very strong appeal of the movie itself...while Logan is now poised to see how its current hype will translate into a much stronger appeal at the box office compared to what has been originally projected.