As much as a huge Nintendo fan as I am, honestly I don't like that idea either, because of one thing. Nintendo is notoriously stingy, and overprotective with their properties.
If Nintendo bought Sonic, then they will cancel the Sonic comics, the upcoming Sonic movie sequel, and possibly the Mobile games, and other things.
Not to mention, take Sonic off STEAM, the Playstation Stores, and such, limiting his audience, and some Sega fans hate Nintendo still.
In fact, nearly a decade ago, Archie Comics actually approached Nintendo with a pitch for a Super Mario comic, and possibly a Kirby, and separate Metroid mini-series. (Artwork from the pitch can be found online drawn by Sonic/Megaman comic artist Tracey Yardley.)
Supposedly, NOA (Nintendo of America) liked it, but Nintendo Co. LTD turned it down, no questions asked…
They'll let Mario be on Campbell's Soup, and underwear, but won't allow him in any American comics, and not even an animated show sense 1991. I really don't understand Nintendo's licensing department & policies…
(As for the upcoming animated Mario movie, that's been in "Development Hell" so long, I'll be surprised if it ever gets made, and it wouldn't surprise me if Nintendo cancelled it, like their cancelled Metroid movie.)