Wall of text ahoy!
There HAVE been Sonic manga before, but they've mainly been for short runs and very slapstick and comedic in tone. (Also most of them are rather difficult to find since they're all out of print and most of them haven't been collected in tankobon or any other format. There have been translations, but they're ALSO hard to find.
Having an ongoing less comedy focused Sonic manga would be pretty cool but if Sonic Team and SEGA agreed to do it, they would:
Probably end up going with a Japanese mangaka. I don't think I've ever seen =
A-R-Q refer to himself as a mangaka before and since Sonic Team is based in Japan, it's just more convenient for them to keep in touch for the long term with people that work locally. In most cases, submitting unsolicited material to, well, any entertainment company is a bad move since most companies don't allow for it. Not to say that there hasn't been any situation where a Sonic fan has come up with a proof of concept for something, sent it to SEGA and SEGA approved...
because there has. They had a working proof of concept and a specific idea of what they thought SEGA could do with it, though. The likelihood of SEGA/Sonic Team going "LET'S DO A SONIC MANGA" based on an unrelated comic that has only released five pages so far, was made in the UK and was purely intended as a fancomic is much, much lower. If it did happen, that would be amazing! OAO!
Have to contend with Sonic's lack of mainstream popularity in Japan. It's not that Sonic is obscure, it's that compared to his presence worldwide, Japan doesn't really "get" Sonic like the rest of the world. For example, Sonic X, the anime? The only reason it got two more seasons was because of the overseas ratings, the series bombed to the point where (as I recall) Season 3 was never broadcast in Japan. They had some online release for it, but that was years after. Meanwhile, the whole series is still airing on broadcast TV in the US.
Not saying it would never happen (I hope it does!), just saying it's not really as simple as showing somebody's stuff to SEGA.
Of course, where Sonic Team can't deliver, the fans do, so be sure to support the Sonic fancomics/fan manga/doujinshi/Sonic the Comic Online/whatever the kids are into these days that you enjoy! <3