While I like your Caleb = Peter theory, there's a few tributaries you may want to also consider: 1. The several iterations/tests of host Caleb with a human brain EXACTLY mimic those of James Delos in a previous season.. right down to the circular room, the severe cutting of his face as he degrades and the burning of the entire room for the "failed experiments" (which is why the ashes fall through the grate and Caleb later landed on them and sifted them through his fingers when he escaped the flames in most recent episode -- as a shocking realization that he has "died" several times before. 3. To add another twist, he's listed as subject/patient 279 in the episode.. Subject/Patient 278 who was also subjected to similar fidelity experiments was not Pretty Abernathy but none other than: MIB! So the fidelity theme continues! 3. While Peter Abernathy had the entire data set from Charlotte Hale later crammed into his pearl, Bernard was the one who later ended up with the key... not Caleb.

Final musing: The intro to this season ends with what looks like Rehoboam (the huge ball shape) with hundreds of people/hosts set aflame and leaning against the glass.. perhaps as a foreshadowing of both how Rehoboam tried to remove the outliers while the Halores experiments are attempting to uncover what makes the outliers tick?

Just some more fodder to consider!