This is definitely one of the worst updates I've seen so far.
Having questions close after a period of inactivity is a good idea. 48 hours is not long enough as some people don't hit the site every day, and may not be on for the weekend. So I think that's pretty silly. 5 days of inactivity or something would have probably been better.
Closing it after MHO is a terrible idea as well, because a lot of good info can be added after an MHO is awarded. Just because one opinion is the MOST helpful, doesn't mean the other opinions cannot be helpful too. This will significantly lower the amount of help an asker can get, which runs completely opposite of the goals of the site. Bad, bad idea.
The private answer seems like something prone to abuse. It will be more difficult to moderate, and other people won't be able to call out something that is clearly bad or misleading advice. People that reply can be anonymous if they don't want their words associated with their account, but having those words be viewable to everyone ensures that they have some sort of accountability. If you want nobody else to see your answer, chances are high that the information in it is questionable or manipulative. And again, there could be useful information that is now being hidden, that could have benefited other users. So, it lowers the safety of the information while also lowering the amount of information Users get, again going against the point of the site.