[TheOtherHobbes]

This has always seemed like a hopeless star-eyed and wildly impractical idea.

So your robot ship turns up and what happens then?

If it's going to self-replicate it needs to recreate most of the features of an entire industrial civilisation. In our terms that would be metal refinement, chip manufacture, chemical life support and more - all done by bug-free software running on hardware which is perfectly error-free and reliable and lasts indefinitely.

If it's going to seed biological (or equivalent) colonists it needs to be clever enough to find candidate planets with an ideal biosphere and no biological threats. Then it needs to teach the colonists how to survive and colonise.

A lot of SETI and colonisation seems to be based a naive idea that all you have to do is get from A to B and you've solved your expansion problem.

In reality propulsion is just the loading screen. Winning the game is a much harder challenge. So many things that can break, fail, be destroyed by chance, or go wrong because of design flaws that it's an insanely difficult problem without very much more advanced tech.