Pricing of such an animal is an interesting thing because it's so easy for people to then assign a value to "the computer part." In your view that's $300 (if by "under $1k" you mean $999), which seems too low to me. Psychologically if not also from the stand point of the BoM. Feels like the delta needs to be along the lines of $500. Of course they could achieve part of that delta by raising the price of the iMac
I've read your subsequent comments and you're way overthinking it IMO. The 5K iMac starts at $1799. In your wold the value of "the computer part" is
negative $800. Never going to happen.
The only way a standalone 5K monitor will cost more than (or even the same as) a 5K iMac is if the standalone monitor is meaningfully better in some way(s), e.g. higher refresh rate/promotion, VRR, HDR, mini-LED, etc.