First of all let me say: very nice use of thrust and env_joints to create mechanics, always glad to see people go more in depth with their modding.

From just by looking at longchin's replay, the crumbling starts way too late. My estimate would be that the crumbling should star about 300-500 frames after the statue is taken (around the time when the player has passed the first fourth of the bridge) depending on just how difficult you want it.

After the collapse starts, you might want to slow down the rate that the parts fall at. You could also add some thrust to the bottom of the falling objects to make them stabler to run on (see my sky_island mod for an example of the concept).

All in all once you get the collapsing bridge part in order, you'll have a pretty solid mod in your hands. Right now it checks all but one of the boxes for a good parkour mod in my books:
-It introduces a mechanic that let's people do something they couldn't do in the game before.
-It has a well thought out layout where every object seems to have a purpose.
-It's environment makes somewhat sense and isn't awful to look at.
-It doesn't seem to have any game breaking glitches.
-And once you get some testing done and get the timing on the bridge down, it'll also be well tested and optimised for fun experience.

Nice work.

P.S. Only thing i could see keeping this mod from being playable in mp is the amount of frames it might take to finish. Otherwise I've seen people clear a lot more challenging obstacles in mp.

P.P.S. I thought I'd share you some tips I've found usefull in my days of modding:
1. Add someone good at parkour on your steam or skype. I don't think I could have ever made the raid mods, if I didn't have Swexx and Large test them for me at every step (or atleast I would have had to spend time to lean play myself :P).
2. It took me far too long to realise this but, if you're making an interior that isn't meant to be viewed from the outside, like this mod, make the walls to be atleast 100 thick. That way The camera won't pass through them and get blocked.
3. If you already haven't, learn how to make a mod on notepad from start to finish. Modmaker is very useful for getting visual feedback on what you're doing, but it can't do all of the things notepad can. For example in notepad you can add a third decimal to your digits, which allows you to move and scale objects by just 0.001 (I don't think I have to explain why that's useful). Also sometimes the modmaker adds somethings to the mod you don't want, like altering dm_threshold of individual joints.
4. I think you already have this one down, but enjoy the process. Best mods come out when people make them for pure fun of making a really good mod.