For one thing the XboX is a very closed platform run by Microsoft and there is no lack of violent games available there. I imagine this part of the agreement is simply an oversight that will be corrected in one form or another.
The only other possible way that this could play out if MS stubbornly don't want to allow adult content on computers is that anybody who wants to play games will switch to another platform, be it Android or Ubuntu or whatever.
The most likely dangerous thing that this could do for game developers would be if MS took control of launch dates for third party games so that they didn't clash with games they planned to heavily promote themselves or with preferred partners.
So maybe if you're an Indie developer you can't launch a game during the Xmas period if Halo 6 is due to come out or something like that.