Don't know if this is doable, but it would be great if Galaxy could be set to launch other launchers and check for updates in them on a schedule. Otherwise, might launch a game only to need to wait for an update I missed because I'm only using Galaxy.

I'm looking for the same thing, that's what I was interested in with GOG Galaxy 2. Having my games together, and all of them coming up to date. How many times I wanted to play a game, and I couldn't because of an update because I hadn't launched the launcher for too long?
This is THE feature I'm waiting for ^^ Or at least a notification that an update is available on my game. Is it possible?

how it can work in real world? how galaxy would know when is the right time to pop up all of your game launchers at once? maybe when you play some game or watch a movie? :) or downloading something you need really fast?
only you can know when it is the right time to run updates, so why can't you be bothered to do simple clicks, let's say, when you turn on your PC? launch all launchers, let it update if needed, go get some coffee or something.
Why gog have to invent square wheel when solution is already simple and takes no effort?

Going by that logic it's really not hard to open all the launchers separately or hell use shortcuts on your desktop and start menu to launch games

yep. it's not that hard and much faster than loading 3 game launchers in chain :)

the problem is, only steam has some kind of API, Uplay, Origin and others does not have any API so you can't check versions.
steam API is not used in galaxy (it uses your login and just parses data that you can see as user - profile data). developer of steam integration explained it in detail on their github in bugs/issues section.
even if gog can go extra mile and query external service like steamdb to see changes in packages it won't help to add this feature to all games (only steam, and after alot of troubles of parsing steamdb webpages).
also gog hardly has any means to see if any game launcher needs an update, so even if they can partly implement this feature for steam games you still will have to update your launchers manually.

that's why I mentioned square wheel. this quest has no satisfactory outcome even if gog will spend weeks working on this.

Honestly the only thing I really want in this department is for Galaxy 2.0 to show download/update progress percentage/ETA.

Having games update at times other than when I try to play them is one of the reasons that I always leave Steam running in the background even though I now only use it when I can't do something via GoG Galaxy. It also one of the reasons that I think that actually only having one launcher running is unrealistic without more help from the platforms that GoG Galaxy is trying to integrate with. As long as GoG Galaxy is integrating with them without making deals with the associated companies, I rather doubt that GoG Galaxy is going to be able to do much with updates for games from other launchers. It would be awesome if it would happen, but I'd be surprised if it does.