I don't have a super powerful computer, so playing with a render distance higher than 12 is awful with frequent stuttering and fps drops, even with Optifine. However, there's a new mod called Sodium that offers dramatic performance improvements over Vanilla and Optifine called Sodium. Here's a quick video comparing the performance of all three:

Sodium optimizes the rendering engine, but unlike Optifine it doesn't change gameplay because it doesn't have any unnecessary features (eg. Zoom, changing particles/fog, extraordinary render distance, changing the chunk loading ie. lazy chunk loading, dynamic lighting etc.) All of its changes are limited to performance only. Sodium can be paired with another one of jellysquid_'s mods called Phosphor, which optimizes the lighting engine. This helps when generating chunks but doesn't make much of a difference otherwise.

For example, I went from 11-20 fps during initial world load on vanilla to 50+ with sodium. Here is another direct comparison between Vanilla, Optifine and Sodium on my machine:
- 32 chunk render distance Vanilla on default settings. Awful. Stuttering and 1/2-1 second freezes. ~20 fps
- Optifine on default settings (w/o vsync). A lot better, but still has stuttering. Note that some things look different to vanilla (ocean on the far left) ~40 fps
- Sodium + Phosphor on default settings (w/o vsync). Some minor stuttering but otherwise good. ~120 fps

I suggest allowing the two mods for 1.16+ speedruns because of how poorly optimized the game has gotten recently. They essentially do the same thing as Optifine (but dramatically better), and without the potential for unfair advantages. It would greatly improve the buggy and laggy 1.16.1 experience for a lot of speedrunners, especially because I doubt many of us will update to 1.16.2 for the performance improvements because of the bartering changes. Perhaps most importantly, it evens the playing field between those with good computers who can comfortably run at 20+ render distance and the rest of us.

We would if there was sodium/fabric for 1.8 lol

Specifically fabric because forge sucks

Why not make it only for 1.16 runs then(rsg since there isnt any set seed 1.16 cat)

or any of the 1.16 category extensions? Is the reason why it's not allowed because it isnt offered to all versions? and for something to be allowed that is similar to optifine have to be available to all versions?

Especially because performance in 1.14+ is (in a lot of cases) worse than earlier versions

I think using Sodium should be allowed, unless we find something that breaks the game from vanilla gameplay (Maybe on glitched categories..?)
EDIT: We still have to decide if the mod will be allowed, sorry for being misleading

Vanilla 1.14 runs faster than vanilla 1.16 so I believe a mod that fixes those optimization issues in 1.16 should not be thrown out the window.

Something of note:

Sodium (specifically, not Lithium) does apply some graphical fixes to Vanilla. For instance:

These are not generally advantageous to spedruns (fitting with the rules for texture packs), but may be worth noting.

There are of course going to be some minor graphical glitches for the time being. We should report any graphical glitches to their CurseForge page.