This is good but i hope it's really mature, last week i tried enable it on Hogwarts legacy with my Rx 6700xt and the game crashed instantly. I'm on Mesa 23.1, i will test again when 23.2 will release
I think the devs are still working on the release of 23.2.
We probably see it in october / november.
Once it releases the availability depends solely on your distro.
If you are on a fast updating / rolling distro such as tumbleweed or arch you'll get the new packages very quickly (usually days / a week after release)
Even when I used the environment variable, RT wasn't available in many games (The Dark Pictures, Wolfenstein Youngblood). Not sure if this new Mesa is going to change that but I'm definitely happy to see any progress and I'm thankful to all the devs working on it, even though my RX 6700 XT is not powerful enough for some serious RT.