Yup. I'm the one who did the Roblox bytecode exploit that lead to it being disabled: the specific attack there was that getmetatable internally leaves the metatable value on the Lua value stack even if it ends up returning the __metatable locked message, which you could retrieve with a crafted bytecode chunk. I leveraged that into getting the metatable for the global environment, which was the entire Lua standard library, and crucially the same table across Roblox's script permission levels. Roblox used "context levels" for seperating priviledge Lua scripts, which interacted with the server API endpoints, and normal game logic. By poisoning the priviledge context's metatatable with my own functions I was able to capture the server endpoint URLs and accesskey, along with things like send arbitrary HTTP requests to their CDN from the server to steal any place file. This easily could have been arbitrary RCE on their servers instead: the crafted bytecode chunk attack for getting a r/w primitive from for loops was published a little bit before this attack happened, IIRC, but there was a lot of less CTF style writeups about Lua internals and I was, like, 15 and an idiot.

In practice it's really hard to sandbox arbitrary user controlled scripts. Even after this I found a half dozen other bugs in their Lua<->C++ bindings that you could leverage into server code execution. V8 and other browser engines still having JIT bugs and DOM manipulation exploits every other week should terrify any developer who thinks "oh I'll let my users do a bit of scripting".