This is going to sound snarky, but it's not. The MM guild will probably get the same replacement that other guilds have gotten; either a guild-specific 'thing', or simply nothing.

More guilds were supposed to have guild specific 'things' but Kodius has had his life rear its ugly head.

Typically this type of guild perk MMs have is replicated with free techs, which I think MMs have for enchanting?

I'm guessing that moon mage guild abilities aren't high on the priority list since they already have predictions, likely the most powerful and intricate guild ability in the game. Add to this cantrips, backtrace, high sorcery, astral travel, time sense, and sects.

I don't think you could expect to be built in the next decade even if they were of interest. Look at what has already been planned. Bard abilities were announced in 2011. The crowd system, also heavily slanted towards bards, was announced in what, 2015? Trader magic in 2014, let alone useful abilities. Paladins still have no way to train their guild skill, which was aluded to in 2010. Necromancers still don't have transcendance or lichdom since their release 9 years ago. Slips were originally planned to be shared with each guild. 100th circle abilities were originally planned for each guild. That's not even touching the missing crafting systems as a whole, the missing major revamps such as the barrier review, or the gaps in the spellbooks.

I wouldn't say never, but I also wouldn't expect new systems for moon mages... ever. Maybe a new spell here and there, I highly doubt any guild (save maybe necros) will receive new abilities or complex systems all their own.