The integration of messaging and all the other hubs is a thing of the past, so we'll have to get used to it.
The reason given, which is a good one IMHO, is that if FB or other app developers change how their code is handled in the app, then a massive rewrite of part of the OS would have to be done. This would slow down development and the OS and features would always be 6 months or more behind.
I miss those features myself, but the approach taken and reasons given for the change are valid....
I would much rather have an app update than have to wait months for an OS rewrite, which may or may not work correctly....