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I'm not fully bought into disc brakes on road bikes.

I think there are advantages to the design and materials for rims, tyres and innertubes by shedding the braking surface and removing the heat (carbon rims).

But, you've moved a lot of that into the design of the forks, brake mounts, hub and spokes and spoke patterns.

Rim brakes are incredibly light and incredibly effective. Then when you look at the kind of heat that will be generated on a disc if you really are a pro rider coming off a mountain at 50mph+ and braking before corners for a good 20 minutes. Rim brakes are just so damn effective and predictable.

I do think discs will eventually win, and I'm all for pioneers solving the problems. But I can't see discs touching the pro tour for a long while yet.

Are there any UCI rules that specifically prohibit them though?

I've been riding discs on MTB for 10years + now. And in the UK, I've never experienced overheating to the extent of noticeable reduction in brake performance (came close on a 4mile+ descent that gets steeper and steeper towards end with a 50l / 15kg backpack on).

Yes discs get hot, but they can deal with it. MTB's often do not move quickly, 10-25mph so they don't get that much air, but work amazingly well.
Road bikes, on mountain passes are moving quickly, even steep techy descents they are going to be moving a hella lot quicker than MTB / DH bikes. Therefore they will actually reach a ceiling and then cool themselves.
So Personally I don't see discs having a heating problem (even poorly designed tiny jobs like those formulas, though floating rotors are probably overkill for a road bike).

I descend in fear (on road bike, old one with 80s single pull, and newer one with 90s dual pull 105s) from every mountain pass, that my tyres will blow out. Had one blow out (front!) before on a mates bike, thankfully it was open moorland and I came off in a good place, but had it been a tricky bit/ coming up on a car, might not even be here!
Watched a few road races over lakes passes and witnessed 10-15 tyre /rim explosions thanks to overheated rim brakes (1 or 2 were carbon rims / cork pads on tubs).
Give it a few years and discs will likely become fairly popular.

Hope made a set of adapters in the 90s that took canti cables (CX) into master cylinders mounted on the bars/ headtube, were a neat solution, but was next to no lever 'feel', which is a lot of the benefit of discs.