The problem is, there are far too damn many XMPP extensions and too few of them see any kind of real adoption.
XEP-0313 is a modern replacement, focusing on just the things that people actually need. It's implemented in many servers and clients already (see https://www.zash.se/mam.html ). It's still under development, but it's already in active use by many people.
This is why nobody wants to touch XMPP with a ten-foot pole.
Honestly, there's some days I wonder if there's any way to win.
Secondly regarding XEP-0136 support in OF. I did state that Openfire has only recently had 'XEP-0136 implemented across the board'.
Whilst the Open Archive plugin which provided support is a fine piece of work it was an incomplete implementation with only 1-to-1 chats (no group chat support).
I worked on merging the monitoring and open archive plugins to provide support for both MUC and 1-to-1 using XEP-0136. That work was only fully finished a couple years ago in 2013 so think my comment's still accurate.