If you want it to be "free to most users", the cost of data storage and IO will completely dominate over the cost of CPU.
There are plenty of good arguments to prefer Rust over python for a distributed application, but "language efficiency" is not one of them.
Anyway, if you are biased in favor of Rust and want a decent argument to justify it, I will let you use 'It's easier to compile Rust to WASM and have the application run on the browser, while compiling python in a cross-platform way is a nightmare', free of charge.
"moderation duties" and "regular participants" in a forum system have such different use cases, it makes no sense to try to make it work with the software itself.
It would be better/faster/easier to simply build a separate tool that can be useful for moderators, instead of trying to shoehorn it in the existing API. But I don't really think that this is something that really bothers people enough, given that last time I asked if I could get 20 people interested to sponsor the development of the moderation tool, and to this day only one person showed up.