As a Roblox developer, it is currently impossible to get a list of user ids that Opt-In to an experience.
If Roblox is able to address this issue, it would improve my development experience because opt in players are order of magnitude fewer than players that joined the game. Currently in order to send notification to players, suppose we already used the Profile service, we list out all player data key from DataStore. And then blindly send out notification. Then the backend will decide whether the notification is successful or it is blocked due to not opt-in, limit is reached, etc.
If we can directly get the opt-in list, then it will benefit roblox and dev a lot by removing the need and strain to list out datastore, call notification api on non legible players. and save time a lot