As a Roblox developer, it is currently impossible to link to sites other than the five we are currently given access to as social links. There are many websites that are useful to developers and users that are not twitch,youtube,facebook,twitter,and discord.
Some of the websites that should be added and use cases are as follows:
Github:
Allows for you to have some or all of your games code open source so that if you have a community with members that are competent in programming, they can help you with your project by making pull requests with their own additions to the code, without giving your members full and uncontrolled access to your games placefile.
Users can also use the issues feature on github to report problems with your game
Linkedin:
Lets you link your profile or development studio so that other developers can see that your past developments, and what you have worked on in the past
Amino:
Amino is a social platform that, while not as popular as discord, is used as a social platform by many roblox users Example: https://aminoapps.com/c/roblox/home/. Developers can make their own amino, where they have moderation and have their users make blog posts and wikis for their game.
Trello:
Lets developers show players a roadmap of what updates are coming and which updates are planned
Devforum:
Link to bulletin board posts that contain better information on the game, images, and all the other features of the devforum
Mixer:
Popular Streaming Site as an alternative to twitch
