Or in game. They can send me a notification that Mod Bingo Bongo and Mod Sausage are doing a QA stream, just whip out a message saying the sysem update is for planned maintenance and will be down for x hours.
The UX for almost everything outside of the actual gameplay is absolutely dreadful and needs a massive improvement IMO. It was fine when it started as a little proof-of-concept, 'lets relaunch osrs for a bit and see what happens' but we're passed that now.
The in-game broadcast system isn't as flexible as I'd like it to be but this is something I'll raise and see if we're able to make it happen in future.
The hope is that maintenance of this nature isn't a long-term/repeating occurrence and is mostly setting the foundation for us to be able to upgrade hardware and address long-standing server issues, at which point we'd hope to see less maintenance like this!