Glad to see a feature like custom servers making a mutually beneficial comeback. I hope this catches on once again. It's basically public test realm on steroids, but instead of testing developer patches they're just watching what we come up with instead and presumably will be able to tailor content or gameplay to what they see we're enjoying, or even enhance it somehow. Probably more effective than the feedback they get currently. And as they've stated, PTR as we know it is mostly to test stability anyway.
Either way, being able to play custom matches publicly, and still get boxes can only be a good thing. It'll bring back (or rather strengthen) the concept of server communities within games as well.
I'll throw in a devils advocate and say that some might be unhappy that the playerbase for the purposes of things like matchmaking in quick/competitive might get divided to a certain degree depending on the popularity of another mode like this, especially if it turns out to be quite influential to the game.
I'm excited to see the community fix CTF though (which is how I'm guessing this is all going to play out). But I do think it needs original tailored maps with CTF specifically in mind, rather than conversions of existing control maps.