I'm scared to look at the abbreviations of campaign names. Is it possible to make campaigns as separate "SRC" levels? For example, check out the No More Room in Hell and Left 4 Dead 2 speedrun pages.

Difficulties would then be a problem, that would create a huge list of campaigns, and they cannot be categorized as "Easy" "Medium" and "Hard" because not every campaign has three dificulties nor they are named like that. To consult the campaign name, please refer to the category rules (Show rules > Category rules).

Is it necessary to give the opportunity to complete each campaign with all possible difficulty levels?

If this is not the case, then instead of choosing difficulty, this can be done by choosing a speedrun category: any% (at least somehow), any% max difficulty, 100% (all difficulty levels? does this include completing the campaign in all ways?), ...

If this is the case, then this can be done with difficulty levels as sub-levels of the level, such as speedrun some level of the world in New Super Mario Bros. Wii.

In theory we could setup Categories scoped to a single level (I think), but existing categories can't be changed to apply to level instead of full game. So we'd have to create new categories for every campaign and then manually move every run over to use the new categories. That sounds like a lot of hassle for what we'd get in return.

But maybe if we had some active runners with strong opinions I could be convinced :)

maybe if we had some active runners with strong opinions I could be convinced :)

Agreed