Ma'afu isn't terrible, but he's limited. His scrummaging (something I did rate, even if many didn't) has improved as well for Northampton, but he was never the fittest player in the world, and has swallowed a cow since moving there.
Kepu, Holmes, Faulkner, Alexander, Weeks are the 1st choicer at each Soup side. Kepu is undoubtedly the standout and deservedly the encumbent, but beyond that there's no obvious option, Alexander has been the long term tighthead but many have no faith in him. Faulkner has been adequate, but isn't as strong as Longbottom, who's a loss for the Force. Holmes is probably too old to return to the fold, although Samo did, so who knows, and Weeks had a very good season, but kept having Hamstring problems.
Then there's PAE, Hoskins, Ryan, R Smith and ???. ??? hasn't played much if any Super Rugby. Don't have a lot of faith in either of the Smith twins personally. PAE is a very good scrummager, and has a lot of ball carrying talent, but is raw and hasn't been able to grasp a permanent starting spot (the fact he's leaving compounds this). Hoskins is the same as Paul, but the arguments against are stronger again. And of course, Ryan is shit.
Who's left beyond that? Both the Allatola's have little Soup experience. Metcher has none. Sio hasn't even started any potential coversion. I don't know who's at the Reds or Force.
I feel the 3 that went this tour will go, given both Faulkner and Alexander can play loosehead, unless Weeks has an amazing season, or Sio has a successful conversion. But it could be anyone.