The ports are just a little extra, that don't hurt and even help RE chances, but they aren't the real argument.
I already express why having a new Capcom rep makes sense, is a company easy to work with, and even eager to do so, and their franchises are beloved and profitable, so there is next to not controversy to add some of their characters to the season pass, and instead a lot to gain by doing so.
And again, either RE8 or Remake 3 or another Spin Off, even Movies, Capcom is ALWAYS working in something RE related, it never pass much time before we heard of something of the like, so it's never a bad time to promote the franchise. The ports have nothing to do with this, even if Nintendo may take the chance to promote them if they have the chance.
Yes, Ace Attorney and Devil My Cry DO have chance to be in the season pass, but even combined they don't come close to the numbers of RE, and contrary to the long debate of Steve VS Banjo, there is next to no arguments agains't RE: Popular and beloved characters, high sales (Capcom best selling franchise in fact), popular both in the West and Japan, by multiple generations since the 90's, a legacy as a Survival Horror as big as DQ as JRPG, and a long history with Nintendo. They just check all the marks.
Capcom doesn't needs an excuse to promote RE, just as they didn't need one to promote Megaman or Ryu, they just promote RE because they make money of it, and there is no doubt it would work for them. Even without anything big announce yet, as I told you, there is always a RE product coming with them, and no doubts they will be more than happy to allow a RE character in Smash if it helps keep the hype going even after REmake 2.
I also think they would allow Phoenix Wright, and Dante, heck, even Amateratsu for that matter if Nintendo ask them for it, they are usually that chill in regards cameos and crossovers. But, as for what Nintendo wants, again, is HARD to argue agains't the benefits of a RE rep.