It isn't only a matter of breakage, but a total revisit of strength and stiffness in the forks design.

A rim brake exerts a braking stress of roughly double the braking G-force applied at the tip with fulcrum at the crown. The normal taper and oval section of a typical fork blade handles that fine.

However with a disc brake, in addition to those forces, we have the local stress imposed down at the caliper. This is much larger than 2G since the rotor diameter is smaller than the rim. That has the lower end of the fork stressed highly in a way that doesn't happen with rim brakes. Even if the fork can handle the load, there's still lots of deflection at the tips (unless the fork is beefed up significantly) which can work a wheel loose.

Beefing up the fork seems obvious, except that without suspension, that would cause negative changes in road holding properties.

Those who don't like disc brakes for road bikes, aren't just retro grouches. They just see some of the complications, and, on balance, feel it's a lousy bargain.

I expect that if and when disc brakes begin to appear on more road bikes, there will be a number of poorly conceived bikes, followed by improved forks that ride poorly, followed by --- you guessed it --- suspension road frames.

There was an old lady who swallowed a fly.....