Roadies have the slowest acceptance to overall bike tech. I'd say about 3-4 years all road bikes plus 2k from the biggest companies will have disc brakes and on 5-8 all the rest. Especially if they can figure out a cheaper cable driven road disc. The "ahead set" style stem was on mountain bikes for easily 6 years before they appeared on road bikes. Funny thing was Trek released the 5500 and 5200 with ahead sets around 1997-8 and the roadies lost their minds and they promptly switched back for 1-2 years just to see them back. Once Ahead Set style headsets took on with the pros and general roadies....the weight reduction, strength, and durability rapidly followed... especially all carbon forks.
Ps...Road carbon clinchers with disc will finally be safe for heavy braking and you might actually see pros use them (may forced by the sponsors though).
Looking back and assuming you've discerned a pattern that will carry forward is a habit many people have, but it often turns out to be wrong
The issue with discs on road bikes is the weight and aero penalty
I can completely see the braking benefits, but for the road use I have these are outweighed, vastly, by weight and aero penalty. And there is then inevitably compatibility issues, which supports the status quo
Right now the industry wants to move customers to road bikes to sell a shedload more bikes, but faces the blunt truth that they are lower performance for many people uses
On the slow acceptance point ... the assumption it's always slow with road should also be challenged, ignoring Mavic Zap which is an outlier, electronic has been taken up pretty quickly, as have carbon clinchers, as have aero bikes and helmets etc etc
Stiff, Light, Aero - Pick Three!!