This isn’t even a thing though. It’s not an ETA. It’s an estimate time in which you will join a game. A game lobby. This isn’t even dependent on the Teleport feature at all. It’s dependent on matchmaking. So basically however you are putting together matches is how you would tell a player how long the wait may be. How you’d do this is by finding the average time it takes to find/put-together a match. Teleport has nothing to do with this. You can’t ETA when someone will join a game. Their internet depicts that. Sure you can come close by using ping. But in triple A studios its still dependent on how beefy your computer is because the game has to load all the assets required for the level.
This is quite different for Roblox however. With StreamingEnabled that would modify the variables a lot both on the game you’re teleporting from and the game you’re teleporting to. A feature request for this isn’t needed.
Universe Scripts are coming soon enough in the pipeline, and you’ll be able to handle ETA for joining a match on your own. As far as having an ETA for TeleportService. You can’t because you’d have to take in account the players computer specs plus ping. Do you know how much technology differs in terms of specs?
If you cannot wait for UniverseScripts however, you can always use the HTTPService, and roll your own matchmaking to get this functionality Though you may also be able to use MessagingService at this point as well.
If you show your own custom loading screen when you teleport players you can easily handle elapsed time (Elapsed time ~= Estimated Time of Arrival).