Yeah there are a lot of big time saves with wall clips. It's easier to do with the big enemies like the horse and bulldozer. You can also clip through the bars in E1M1. I'm not exactly sure how that one works but I think it's the Kejdovec that's pushing you through.
There are probably a lot of clips we haven't found yet aswell, so who knows what we can find? :)
From what I can tell it's just enemies walking into you in a certain way, their hitbox pushing yours through walls since they can't overlap or something idk, if you can get humanoid enemies to do it there's a ton of time save everywhere, but it'll make the run a RNG nightmare, I tried getting enemies to push me through walls with godmode on and it's weird, maybe someone can refine it, big skips all over especially the mines in act 2 if you can get the heads to push you through that door can just go through the train door without getting the train, then there's that one fort stage with the exit right there and a shotgun guy popping out the ground if he could push you in would skip the whole stage
The otters in E3M1 can also push you through the electric wall, as seen in Kovic's speedrun, I don't think there's any major skips for other levels with this though. Edit: my dumbass did not look at the first video
HROT 1.0 has been released and with that, the Worker's Speedrun Committee has, in accordance with standard policy, executed a leaderboard clean slate. Categories now include runs of E1+E2+E3 or single episodes, as well as all 26 levels available as ILs. Good luck with your runs, comrades!