We generally agree, but a couple of nits to pick.
1. The advantages disc brakes have in mountain bikes exist because of the sum of rougher and faster courses, fatter tires and suspension. A cross course will never be as rough and won't be as fast. The 'cross bike doesn't have fat tires or suspension either. (Suspension tears up the courses too)
2. The UCI also set the fattest tire limit at about a 32c tire. Even if there was some constant benefit to discs, the skinnier tire doesn't make discs an overwhelming good now or in the future.
#1 and #2 are critical issues the ignored in the rush to discs. Boom/Nys/Stybar races will not be tilted for/against because one of them is riding last year's cantilever equipped bike.
3. For the front disc, there is the small matter of the disc brake forces loosening the skewer. Unless they put the caliper in a different position, the same problem mountain bikers had will plague 'cross for a while. I make this point to remind readers that the switch to disc will include expensive design failures for a while.
4. The 'properly designed' argument is perfectly circular. I can make almost any design case and rationalize it with 'properly designed.' Ex. A 'properly designed' mountain bike will have 12" of travel front and rear and weigh 7 kilos. How come I can't buy one now?
Sorry to be so combative, no offence intended - it's late here.
Re 1 and 2, the advantage of discs isn't limited to power, they also have significantly better modulation. Yes, they certainly make it easier to brake harder for longer without getting tired hands, but they also make it easier to control your traction...which I believe is what you are getting at regarding the skinnier tyres? OK, CX races are mostly won through acceleration and handling rather than deceleration, which limits the technical advantages for elite racers (just as it has for elite XC MTB which still has linear pull hold-outs, on some courses), but for anyone else, discs are a no-brainer, especially where mud and sand are involved. Just as you say the race won't be won or lost by cantis, I'm sure the weight difference won't be a deciding factor either. And I bet many financially overcommitted privateers would convert - imagine for me the noise of gritty mud grinding against your expensive rims and wearing out the sidewalls of your dugasts and tell me discs are for fools!
Re 3, you're right, it's a small matter. The easiest solution is changing the orientation of the dropout, as a number of fork manufacturers did. While I would be hopeful that lesson has already been learned, I'm pretty cynical about humanity's ability to perpetuate bad decision making, so you have a point!
Re 4, again a specious argument. There are plenty of reasons why you can't buy a 7kg DH bike, and none of them have anything
to do with disc brakes.
We're talking cyclocross bikes, for riding CX courses, experiencing applicable forces. There are no extra complicated suspension designs involved, where maintaining strength (and rigidity) through multiple pivot points acting through long levers is critical, and we're not talking about bikes where the normal use parameters include rock gardens and massive gap jumps. All we're talking about is moving the brake from near the crown to nearer the dropout - there is no magical magnification of forces involved, no kinetic energy created.
Do you need to change the design of the fork to cope with the altered stress pattern? Of course you do. Does this mean you don't optimise the design to remove redundant reinforcing where it is no longer required (i.e at the canti bosses, where forks are beefed up to resist spreading and forwards rotation of the bosses under braking)? Why not?
Does a weight-competitive solution to allow a privateer racer to convert from cantis to to discs exist? No, but that doesn't mean it couldn't be built, if there were a market for it.