Someone on GAF gave their opinion on why Ubi gave it back.
Ubisoft wanted to block other publishers from picking up a potential Assassin's Creed competitor.
In 2016 however, Ubisoft is no longer reliant on Assassin's Creed, and it's incredibly unlikely anyone is going to spend $60+ million on 1666, so even if it comes out, it won't be a real competitor.
They basically stalled until it was a moot point.
Oh well. It's nice he got his IP back, at least. He should just hold onto it until he can fully realise the original idea. That or sell it to Activision/someone similar and really hammer that final nail into AC's coffin once it relaunches. What a shame that would be.