I don't ship it, and thus I don't find it cute.
I also don't think the two of them are all that compatible, either. Rainbow's drive for competition would annoy Sonic (who, despite what people may believe, isn't competitive very often), and with Rainbow being the extrovert she is and Sonic having a tendency to pull disappearing acts, it would cause a lot of strain in their relationship. Sonic likes to be a free spirit, and Rainbow more so needs someone who's willing to dedicate time and attention to her, while at the same time understanding if she's busy due to her passions, and while Sonic could certainly fit the latter just fine, the former might be difficult for him. In other words, Sonic would have issues with commitment.