How it will work?
People can use any texting program, notepad, sublime, vscode, etc.
They will write a script and name it something like (part.js) Then when you create a script in Roblox studio, you will have the option to upload files.
Some problems that it might have
As some people are experts with other languages, people will create some pretty amazing stuff, but it will sometimes go too far, that the game won´t be able to handle the scripting langauge and crash.
People will be able to create viruses with it, since roblox lua doesn´t allow you to create viruses with it.
I hope that Roblox in the future creates something like ¨Roblox JS¨, because people don´t want to stick with roblox LUA, this also might lead into new amazing games being made!