What if there's a billion year cycle of slight expansion and slight contraction? How could we ever notice that when we're in the expansion phase of the cycle?
Well, the problem there is that nothing in the standard model would create variations in the expansion rate once you're past the very, very early universe (inflation theory, condensation of matter, etc). If we conjecture that there is a cosmological constant, we can conjecture that perhaps it decays, and perhaps we can conjecture that it could vary, but in reality we're just piling up assumptions and writing speculative science fiction instead of physics research.
We might as well speculate that FTL travel is possible, then that it requires a warp field, and then that highly-traveled regions of space start suffering from space-time distortions as subspace starts to break down.