I think it would also greatly help if we could get some more graphics options, like the ability to turn off post processing client-side.

yes all we have for worlds is "size", i have seen some sub-100mb worlds that are full of sky and water shaders and run like ass (15fps).. this would be a definite "performance" if a small world is cramped with models and high detail shaders that make it run hard and hot for players.

The idea is good,

but the Implementation can be very tricky without a proper benchmarking.

Best thing would be: A bot on a real machine runs arround in the world and collects performance data.

That would be a nice way to make VRChat teach world makers how to optimize their stuff. VRWorldToolkit already gives you some tips on how to make your world optimized, but that's enforced by a curated package not the SDK, so there's some very basic stuff, for example, realtime lighting, realtime reflection probes could be checked by the SDK and warn in the SDK.

There are too many factors that can impact your fps in a world, alone udon can be very slow. There are too many things that can't be measured so It's just impossible to rate.

Maybe this could be implemented in a way that users can voluntarily allow hardware specs and average fps in a world to be sent to vrc. Then other users with similar hardware and settings could know what to expect when joining a world.

it wont be consistant as theres to many factors that make low fps not just number of draw calls

I think there are a lot more things in worlds than on avatars that cannot be described by simple numbers or false/true statements that affect performance of it. Even realtime lights in worlds can be setup in a way that will not drop your frame rate at all and still give you reasonably good looking shadows on avatars.

This would be a lot harder to give even somewhat close to accurate results. Due to more tools being available in worlds, even huge and complex worlds can perform way better then average ones. There's gazillion of factors involved, the avatar system itself is only a rough estimation, especially that it also counts disabled objects due to not being able to detect everything.