CodeBlue_
Smash Journeyman
Guest characters generally don't get special treatment and are only added themselves because they are icons to their respective series. I have a lot of doubt that Sakurai would put in a second Sonic rep, when we consider how he has treated the series and how third parties are treated in general.No, it isn't impossible, to say so is ignorant and silly. Sonic isn't just any guest character.
It appears to me that Sakurai just threw Sonic in as an advertising ploy. Consider the fact that the only Sonic stages we have now are the first levels in their respective games (implying Sakurai is only taking this series at face value) and the fact that Sonic was given an extremely uncreative and horridly bad moveset in Brawl. We can't also forget that only one Sonic track was remixed in Brawl, and that was an instrumental version of His World.
Even if Sakurai would even consider the possibly of a second rep for a third party series, (which I have doubts he would considering he wants to focus on Nintendo characters) I don't see a Sonic rep that would be likely or even acknowledged by Sakurai.
Then again, calling it impossible is absurd.