OK, here's the Good:
-Nintendo and Ubisoft are on great terms.
-The 2 companies have collaborated in numerous games, and Ubisoft was very successful on the Wii.
-Mario and Luigi costumes in Rayman Legends; Rayman, Globox and Barbara trophies in SSB4.
-Mario X Rabbids bodes well for the Rabbids but indirectly bodes well for Rayman.
-Sukapon's an Assist Trophy. The only other limbless character to threaten him was deconfirmed quickly.
-The Smashified hoax warmed up a lot of people to him at just the right time.
-Other non-fighting game characters guest starred in fighting games, and they're in Smash: Sonic, Pac-Man, Link, Mega Man. Could be a similar case for Rayman.
The Bad:
-Rabbids overshadow him. Their game indirectly boosts his odds, but they directly boosted their own.
-Rayman's currently dormant.
-Brawlhalla calls into question his likelihood. We're currently not sure if this is a consolation or unrelated entirely.
-While other non-fighting game characters made guest appearances, the timing of Rayman's is very suspicious. Nearly a month before SSBU comes out; the other characters made guest appearances years before the SSB they debuted in.