If we consider 1E and 2E AD&D to be compatible, which personally I do, then I'd say "Yes", which is how I've voted.
Even in the playtest material we've seen there's already considerably more difference between 5E and 1D&D than 3E and 3.5E, but we're still well within tolerances for 1E to 2E.
I think in practical terms you could probably run a 5E adventure with 1D&D PCs, for example, without huge problems (based on how 1D&D is currently looking), or vice-versa. You could also have a mixed party of 5E and 1D&D PCs, but I feel like 1D&D PCs are generally going to be slightly more effective - then again, the same was true of 1E and 2E PCs.
Yeah that's the question. We don't have any evidence yet (unless a packet just dropped and I missed it), but it seems to me that they may well do this. If so we may end up with a 1D&D that's less compatible with 5E than 2E was with 1E, and that would be stretching the definition of compatible somewhat, I feel.