I think it's fairly obvious that Jihan is simply tired of dedicating his entire time to the company, and he trusts the engineering lead (or whatever his position was) to not mess up the time consuming tasks.
The future direction of Bitmain will still be dictated by Jihan.

I think the most bullish aspect is that they didn't simply file for an IPO for 10 billion instead of 16 - which they would have succeeded at. Jihan clearly thinks that the IPO investors are underestimating the price of crypto and is willing to wait enough to prove them right. If he is correct, this is bullish for all of crypto.