> There are solutions to GR equations which allow for spacetime to be bent to the point where something that *looks* like FTL to fall out, but they tend to require exotic matter, and there's no evidence to suggest that said matter exists.
This is the big one. Alcubierre's metric has been heavily optimized over time to require energy amounts that could be feasible one day, but the exotic matter bit is the second problem. We can only hope that (a) exotic matter exists (b) an alternate solution can be found (perhaps something based on dark energy once it is understood).
As for the frame of reference, perhaps this isn't such a big deal. If for example the many worlds interpretation is valid, and a causality violation leads to some sort of breakdown of a universe, then you simply would never notice them, since the universes where the violation did happen just cease to exist. So, if a spaceship FTL-flies from A to B, B is a planet in movement relative to A, and the ship FTL-flies back to A, perhaps in the "surviving" universes it flies to A slower for example.
It's all hypothetical of course, but it shows that the causality problem could be circumvented.
Then again, we shouldn't be talking about FTL if we don't event have (relatively) cheap and commercial mass transportation to LEO and beyond yet. The sun won't increase its luminosity to lethal levels for the next 700 million years or so, so we have time.