OP,
Tough call. Many bring their personal bias into the buying decision. I also believe it really depends on the racing venues you plan...are they mostly flat or do you plan on a fair amount of climbing and high speed descending.

Probably the most authoritative response to listen to is that of Psimet...who is a wheel builder and sees shift in trend more than we do. Fast guys I ride with are mostly on rim brakes...just about all of them. I believe you will still see a lot of rim brakes in this year's TdF coming up in a week and probably more disc brakes in the peloton as well as disc brake bikes become more prevalent.

I don't really buy into next 5 years owning a rim brake bike is going to be an issue with finding parts. Next 10 years things will likely change but so too maybe rotors, spacing and related bike design elements could you, me and others to want the next best thing.

Can go either way and why many leading manufactures offer both...like say another bike you could race competitively...like uber light Emonda SLR...or you could ride a Tarmac S-works that is offered in rim and disc.

Good luck with your racing. I am sure you will be fine with either choice. Probably a jump ball what you decide right now.