I read about this a couple of days ago and I'm even less sure as to whether it's legit or not than I am regarding most reports/rumors. On the exact same day I read this, I read another report stating that Sheamus was going to be among the top babyfaces pushed in the company over the course of the rest of this year.
On the surface, Evolution does seem like a bit of an odd fit for Sheamus but, at the same time, Evolution has...well had to evolve I suppose since their return in 2014. During their first go around over a decade ago, there really weren't any other factions going on, at least none that were any type of a threat. Evolution members today are over a decade older, one of their former members is in his mid 60s & is no longer medically cleared to wrestle and they're up against another 3 man faction that are every bit their match inside the ring. Apart from Triple H due to his role as C.O.O., you don't see Evolution riding in limos, wearing expensive suits, sitting in fancy eating establishments surrounded by gold diggers, etc. With Batista leaving soon to begin promotional work for Guardians of the Galaxy, maybe not even coming back if there's any truth to the various reports about him being "screwed" by WWE management, they need someone to step in and fill Batista's role as the bruiser of the group.
In that respect, Sheamus strikes me as a good choice. Also, and I think I'm not the only one, it's time to alter Sheamus' character to something more along the lines of how he was when he first showed up rather than a jovial, good natured Irish galoot. Is Sheamus an ideal fit? Not really, when you consider the whole evolutionary motif of Evolution. A decade+ ago, Ric Flair represented the past superstar, Triple H was the present while Randy Orton and Batista were the future. Now, Triple H strikes me as more of the legendary superstar of the past with Orton as the present star, so they're missing someone to step into the role of the future. Ideally, it sounds like a role that'd be tailor made for a member of The Shield. If the reports of The Shield staying together are true, however, then it's not gonna happen. It's not out of the realm of possibility that someone from NXT can be brought up to the main roster and join the group, though that depends on how long the group will be around. More the likely, Triple H will probably hang up his boots until WrestleMania once SummerSlam is over, so it's possible that the group could still be continued with him stepping into the role of a mentor while inducting several new members into the group alongside Orton and Sheamus.