• In a nutshell, there is now an arbitrary limit on the number of category and subcategories you can have on a leaderboard until some or all categories/ subcategories are hidden behind dropdown menus. This comes off as very condescending from Elo, taking control of how to format leaderboards out of the game moderators' hands. More discussion here
* This obsoletes the "miscellaneous" category feature, because once all subcategories are hidden behind a dropdown, there is no distinguishing the subcategories the game mod designated as miscellaneous, and the subcategories Elo decided to hide. It's just so annoyingly bureaucratic! /rant
• People talked about how we need the ability to selectively apply subcategories and categories to some, but not all levels.
I'd also like to point out that currently you cannot apply subcategories to one specific subcategory, although you can apply subcategories to one specific top level category. More explanation here.

This brings me to my next point...

Terrible page layout utilization

So, why are speedrun.com leaderboards so crunched for space (apparently) that we need dropdown menus for everything now?
• Answer: Elo needs to make more money from ads. Need I say more? Look, I get Elo needs to make money, but surely there's a better way to position ads that doesn't involve wasting a ton of space on the left and right of the screen, which could be used for meaningful information like more room to list categories, etc.

Ok, I feel like the OP didn't really elaborate on what "better IL support" should entail, and I play a lot of IL speedruns, so I figure I will elaborate

IL table problems
To be clear, this is about the "view all levels" leaderboard table, for example: https://www.speedrun.com/hitman_3
• Problem 1: The IL table can only show up to 4? subcategories until you have to use a scroll bar. As can be seen by this monstrosity. Now, a scroll bar in and of itself isn't a huge deal, but the UI on the table with scroll is terrible. You literally can't see the top column labels once you scroll down the table a bit, and you similarly can't see the row labels once you scroll right, meaning I've had to add "placeholder runs" to the Hitman 3 Extensions leaderboards, which is kind of ridiculous compensation for bad site design.
* I've proposed a few solutions to this issue here. Namely, utilize space on each side of the table better (probably won't happen due to Elo loving ads), or add row/ column labels that will scroll with you.

• Problem 2: The IL table only shows the "default" category of IL runs. Ex: You can only see PC runs as default here: https://www.speedrun.com/rogue1/levels
You should be able to toggle between subcategories and be able to see all IL console runs on a leaderboard table for a quick summary, instead of having to go into each individual level to see the console record. That's just inane. More explanation here.
Being able to toggle between subcategories on the IL table would also help a lot for organizing leaderboards better to avoid the issue of having to have more than 4 columns of categories to begin with, thus avoiding the scroll bar issue above.

Miscellaneous IL problems
These aren't huge issues, but the sum total of these oversights really makes me feel like IL's are discriminated against here.
• Why does the "active players" stat in game statistics not count IL runs? Are they deemed lesser by Elo? Example
At the very least, please separate out an "active full game players" and "active IL players", similarly to how there are separate "recent IL runs" and "recent full game runs" stats.
• Why does the "recent runs" widget prioritize the category of the IL run over the level it was played on? I feel like if I had to only have one category or subcategory to go off of, I'd want to know which level a run was performed on, vs knowing if the run was any% (example) category. I literally cannot comprehend any info from the recent runs widget when it comes to IL runs.

• We really should get ability to have separate timing methods for IL vs full game, this is long overdue
• There should be option to only have in-game timing/ loadless timing, without also having "real time" tacked on. Some games are just IGT only, why is real time forced onto it needlessly? Coming form someone who has to edit out false "real time" submissions for eternity for IGT games.
• Even when IGT is the default timing method, the real time is prioritized when you click on the run, as seen here. This is strange, especially because when using RTA loadless, the RTA loadless time is shown first over the RTA with loads on the run.
• Ability to mass edit runs would be so helpful as sometimes you decide later down the road you want to switch timing methods.

• Why did Elo remove the website and discord server labels? You can barely see those tiny little symbols now. Also, labeling the website gave much needed context to what the website was, so the player knows if the site is worth clicking or not.
• At some point will other games besides the sponsored one (Severed Steel) get the option to have multiple Discord servers linked on the page? Ex: https://www.speedrun.com/severed_steel Or is this a pay to have feature? Seems discriminatory when only this game has it. Many other games have multiple speedrun Discord servers for one reason or another and could use this.
* Note that you can't even tell which discord server is what on the Severed Steel page due to Elo removing labels on them... nice...