Yeah, if Smash got a Type/Moon character I would think it would have to be Archer, since Saber has official porn of her out there.
That said, a TYPE/MOON rep in general is still unlikely just due to FATE being very NSFW sometimes.
Aside from the H-scenes(which were cut out in the remakes), Saber is very very SFW. And CERO does not care for crossovers that come from NSFW series as long as the content from those series coming to the crossover is SFW. Otherwise, I'm positive Bayonetta wouldn't have been in.
Plus, part of the reason those H-scenes existed was, at the time, they felt like they had to do them because most Visual Novels at the time were following that trend and were worried about Fate/Stay night not selling because of that. When they saw they didn't need to afterwards, the scenes were cut in the remakes.
Because of them going away from the NSFW nature(at least, the H-scenes. Not always in terms of
fanservice), I think Nintendo and Sakurai would be fine with them. That's not including Fate's massive popularity in Japan and the fact that Grand Order has become one of the highest grossing games.
I'm afraid It would have to be Shirou.
It WILL be Saber. No exceptions. Saber isn't just one of
the most popular characters in Japan, to the point where she's consistently in the Top 5 Most popular Female characters. Her artist And creator, as well as one of the founders of Type-Moon, is very passionate regarding her. She's practically
their Waifu. And the other Type Moon creator is also big on Saber too. If Fate gets a rep, it WILL be Saber. Takeuchi and Nasu would both make sure of it.