My wife is definitely hoping that they aren't completely sold out for the 10k. I would guess that if anything was sold out, it would just be an allotment maybe for the hotel. GET Sports for US travelers isn't suggesting they are out of any of their entries to my knowledge; we were originally going to book through them until I came across the info about bibs-only being right around the corner.
Our hope for now is to keep our hotel only registration, buy discounted tickets from another third party source, and register for the challenge -- this method will save us more money than the cost of both races for the both of us if we can do it. If the 10k entries aren't available when bib-only launches, it sounds like the travel providers may still be a source to go with and just forgo such savings though -- assuming they don't then have the option of selling things off individually to avoid being left holding the bag.
Fingers crossed "early June" doesn't leave us wondering for much longer!