Being the majority of braking power is at the front wheel, would it make any sense to retrofit a roadbike that you love with a disc fork and front disc brake but leave the rear caliper brake?

works great on lots of Mountain bikes...

do you feel that the present brakes on your bike are inadequate? if no, then leave it alone, and slip some new tires on instead! if the brakes have gotten worse over time, and were fine originally, slap some new Kool Stop PADS on it.

you can only use so much braking force......, then you move on to unscheduled Ballet performances in intersections, and trips to hospitals.

First thing you have to ask is do you really need better front brakes or do you want better brakes?
If the brakes you have are properly setup , yet inadequate then you need better brakes. A wet road ,traffic, steep hills require judgement and reliable consistent brakes that you trust and know.
If you had no brakes you would cycle much slower, walk down hills not up them and could still get caught out the same as if you had very good brakes and cycled faster.
But at the end of the day you have to be able to trust the reliabibity and consistency of the brakes.
The pro's use rim brakes on mountain roads at high speed, albeit the roads are closed and they are getting paid to do it they must weigh up the risks involved and ride accordingly.
Would you buy ceramic discs for your family car so you could drive a little faster or just drive carefully and trust the car makers original judgement.

I am trying out the same thing.

I have a similar mixed setup, with hydraulic RIM brake (Magura HS-33) in front and a conventional cantilever in the back, on one of my bikes. I like the way the balance between brakes works out.

These analogies are a bit misleading.

First pro riders use rim brakes because the UCI has, so far, not permitted disc brakes in the pro peloton so they have no choice. That seems to be changing and discs may indeed appear on pro bikes in the future, particularly for mountainous races and stages. They are already nearly universal for cyclocross racing.

Second, ceramic discs for automotive use do not give shorter stopping distances or more braking power for regular driving. They are used because they prevent fade in very heavy, repeated brake applications as in racing. They still work when red hot when iron discs do fade. The next time you use your brakes that much, consider ceramics. Otherwise save the money.

You've got that one wrong. The UCI does permit discs. The CPA (Cyclistes Professionels Associés) has called for a ban on disc because of injuries suffered in mass crashes.

Considering that a rim brake is a disc brake with a really big rotor, it makes little sense. I have a mountain bike with a disc on front and linear in back and I can't tell the difference. I only had to go that way because suspension forks for linear brakes with the travel I wanted aren't made.

On the other hand, I have numerous bikes without disc brakes that stop every bit as well as my disc equipped bikes. Those include bikes with dual pivot, cantilever and, until recently, linear brakes. These bikes are all different flavors from road to touring to mountain bikes. Being able to brake has never been a problem even on a loaded touring bike on a 50 mph wet mountain downhill. However, I do choose good brakes no matter what flavor I use.

My commuter is (so far) front disc only.
I’m quite happy with that.
Better braking in the wet.
Less hand effort for a given amount of braking is nice too, particularly during winter.
Hopefully I’ll get around to doing the rear conversion before the current rear wheel calls it quits.

My current dual pivot brakes have good stopping power as long as conditions are warm and dry. I have had times when the rims are slopped up due to road and weather conditions where braking has been less than ideal. I'm also concerned about the grit in these conditions wearing on my rim compared to an easily replaceable disc. I've also experienced conditions in the spring and fall (like now) where the air temperature is just a bit below freezing. The roads are wet but the spray onto metal surfaces freezes, the rims being the most affected. In these conditions I was wondering if the disc would stay cleaner and drier thus improving braking while sparing my rims from the abrasive action of road grit.

If the added bonus was finer modulation the rest of the year . . . win/win.

I'm not planning on doing this just for the sake of doing it, but if the fork ever became damaged and needed replacement, I would consider the conversion if it made sense. The wheel is no big deal as I like building wheels so building one with a disc hub isn't an inconvenience.

Not really wrong. For a long time the UCI did indeed ban discs. Then in 2016 they allowed them on a trial basis and backed off their approval after the Paris-Roubaix injury that the CPA claimed was due to the disc. At this time, I believe the UCI, at the CPA's insistence, still bans discs.

Suffice it that pro road racers do not use discs, not because of their braking inferiority, but because of safety concerns.