As a Roblox developer, it is currently unperformant to run Luau code within an experience that users create in those experiences.
Capabilities was a step in the right direction, but theres issues with loadstring besides just isolating the environment.
Most notably, performance. Luau has a mechanism to deoptimise certain bytecode operations if the environment is tampered with, loadstring is considered to be a function that tampers with said environment (somehow). One of the major losses to this is fastcalling.
If Roblox were to address this issue, it would improve my development experience as I could create educational experiences, or puzzle games involving Luau as a language, without needing to worry about a major performance loss caused by the lack of FASTCALL functionality.