I'm not suggesting for you to be confined to spring infra, I'm suggesting that whatever you distribute outside of spring infra is also made available on spring infra.
But the end result is the same.
This is so that other game release teams/persons that do not wish to hide other games do not have to scour itch and steam for your files so that their players could also experience your game.
If you went and downloaded evo via springlobby, your experience will be fundamentally subpar compared to if you had grabbed it via steam or itch. This seems more like a filtering issue on your end. You want to be able to filter out things that you can't access from directly within spring's infra.
NOTA does what it does because they want to be special with their closed-source client. They also have their own lobby server if I understood correctly.
Everything that you said here is incorrect. The client is not closed source, and hasn't been for many years(4?) at this point. They also use spring's ubserserver server.
I also don't see why I should have to do XYZ and PQR as preconditions before I can dare to suggest THIS improvement. And I am already going to the trouble of providing a good experience to them in multiple ways, including opening this topic and requesting this change to be implemented. This change is also not a replacement for making game distribution packages and is not related to those in any way.
The problem is that what you want would not actually improve the experience. It would simply extend a broken one to not be quite as broken. It's still broken!
Rapid wasn't created with the intention of it being used as a distribution system apparently(which was certainly news to me, but this was stated semi-recently by either abma or kloot, iirc. I'm pretty sure it was kloot in response to a BA thread regarding rapid.). As a result, I wouldn't recommend hanging all my hopes and dreams upon it. The test branches are certainly useful, and the updating of rapid is super useful and saves me a lot of time and trouble in the long run. But just understand that the way we use it was not it's intended use (although I don't understand why).
I'm telling you that your suggestion is flawed and that what you want wouldn't necessarily help matters. As far as I can tell, what would work for you best would be a special battle filter. Your suggestion might simply just add an ineffective bandaid to a wound that refuses to heal.
Edit: I'mma stop replying at this point because I don't think I'm helping matters. Perhaps someone else has a better perspective and can articulate it in a way that is less confusing than I.