I wouldn't feel like the "meaning of life" would be answered if we turned out to be brains in vats or whatever created with a specific purpose in mind. Notwithstanding the fact that they obviously have a lot of power to punish or reward me, why should I even care what they think?

To me it seems the answer would have to be an independent ontologically basic intent, but then I'm not entirely sure I should care about even that. So a satisfactory "meaning of life" might be impossible even in principle, which I think gives a lot more credibility to the existentialists.