Vertical Support

In the pull closet you would vertically mount a piece of wide enough ladder rack right above the sleeve/slot that leads to the MDF floor. Depending on the cable counts 12 or 18 inches wide may do. Then you'd bundle the cables into manageable bundles of 30-40 some and tie the bundles individually to every step of the ladder with Velcro straps. It is nice if you can make the bundles criss-cross so the cables are not always exactly vertical (meaning the friction that holds them from slipping down is higher). One other solution that we have yet to explore here on bundles of 4-pair cables, is to use those pass-through "Chinese Fingers" grips and clamp the straps to the steps of the ladder rack.

The turning point can be handled by using 90 degree outside bend or "waterfall" ladder rack accessories. Actually 90 bend is better as it has steps of its own, to which you can Velcro-strap the bundles to distribute the load.

Good luck with your install.

Just a layman's perspective: wouldn't the velcro be loose enough to not have enough holding power? How about a spiral ladder rack? It would use more cable, but would definitely have more supporting power. I think the real solution, though, is to do straight, but use something that is definitely going to hold well. I'm sure you're right, so I just must be missing some detail about the way the velcro works. Perhaps it can periodically go horizontal briefly with two connected or nearly connected 90 degree accessories every so often to really hold it in place, or periodic circle/spool accessories (one or two wraps would be sufficient?), but that's just because I can't envision velcro doing the job, which, obviously, there is a strong claim that it does. I think I'm being overly paranoid, but that's my right, as a layman. (I haven't ever experimented with a fish scale and vertically supported cables.)

You can actually tighten Velcro pretty tight if you want/need to, and yet, due to its width, it will not crush the cables. On the ladder rack you would have steps every foot, so it's pretty many 8 points per every floor to create enough holding power for the bundle. Any change in the bundles' position from the ideal straight vertical will actually help to increase the friction, so you may want to criss-cross the bundles or at least make them "oscillate" i.e. let them bend a little inside the space between the ladder rack's steps to break the vertical.

Pardon my ignorance, I've never heard of a spiral ladder rack. Is that a particular product you are referring to?

The idea of wrapping around spools is great, but I think it will make it really difficult to add any cable, as well as to pull the cables in the first place. Besides, this way amount of weight supported should be limited to the cable's maximum tension, which is not so great for category cables - about 25 pounds. I mean, 25 pounds of weight buys you a lot of

4-pair cable, but in a bundle several cables can be supported by a single most stretched cable, which is dangerous for the cable.