Certainly possible, yes. I’d be fairly surprised, though. Yes, if a CRQC becomes realistic there may be an incentive to hide it so that you can complete it and go steal a bunch of bitcoin, but generally conspiracies don’t really scale - it seems to me it would be incredibly unlikely that a large team of expert scientists (not to mention investors and executives and support staff) would not be able to keep quite that they’re within shooting distance of a CRQC. More generally, while it’s possible that this happens via some huge breakthrough, that isn’t what we’ve seen so far with QCs - they’ve been very slow deliberate progress iterating in small public steps. A startup making good progress for 5 years then suddenly going dark without shutting down may well also be an indication of something.
Ultimately this gets into the “it’s hard to speculate what a future community might do” because there is so much detail to any potential scenario that would go into such a decision. In my (fairly strong) opinion, the community is likely to have enough information to be relatively confident that a CRQC is highly likely at least 1-5 years prior to it existing (where the range is mostly uncertainty about the rate, not uncertainty about the state of things), but it certainly could happen that I’m wrong. Ultimately we can’t decide for the future community, but we do need to at least somewhat predict what they’re going to do because it’s important to understand it to help us decide what to do today to prepare.
This all somewhat ignores the possibility that a government gets a CRQC first. I’m admittedly not incredibly concerned about that, both because so far it appears the most advancements have been in private companies willing to throw money at this, but even if that changes, a government leaking that they have a CRQC by stealing Bitcoin doesn’t seem super likely to me either.
