> rocket engineers/scientists are in high demand with lots of likely sponsors for immigration

I wouldn't be too sure about the immigration part, when even a software engineer hire for a defence/defence adjacent job requires jumping through a number of bureaucratic hoops of security clearances. Even the companies with deep pockets don't always get the best people in the world -- they just get the best people that HR can actually hire.

That's often true, but less true than it was a decade ago. Private, commercial space companies are a lot more numerous now. Sure, most of them have military contracts/oversight as well, but there are more opportunities with them that don't require military/government certification/authorization of immigrant hires than there were previously.

Also, there are plenty of space companies that aren't in the US/UK/China who are hiring (and more willing to work with non-domestic employees since they're playing catch-up), and plenty of companies in US/UK/China who employ contractors that aren't subject to the same hiring restrictions as the first-party/defense-contracted company.

There are a lot more specialized/high-expertise roles here than the ones critical to a nation's space program (or fungible with making weapons). Random examples off the top of my head include crew/life support expertise, launch facility engineering, LEO consumer telecommunications, and more. Space hasn't been fully commodified/detached from government interests--not by a long suborbital burn--but it's moving that direction enough to thaw out the ability to immigrate for work a bit.