The only problem i can see to the early access of PoE is that compared to D:OS it will be a short game since it will only be a little bit longer than BG 1 and BG1 WAS short, and now people are used to having a lot of content in their early access, enough to please them for months, I don't see those who pay for early access enjoying having to pay extra money for the 5/8 hours of gameplay we currently have in our beta especially those who played the early access of D:OS or Wasteland 2.
D: OS is such a long game (70 hours to finish it if you aren't a completist on your first playtrough yep!) that it could afford putting the first map (and there is a LOT of content on this first map) for it's early access, and unlike Josh Sawyer at Larian they don't mind putting spoilers in their early access.
So how could they create an early access interesting enough and spoiler free without ending up by putting a large part of the sidequests of the final game in order to have as much content as WD 2 and D:OS ? (and in fact unless they redo the entire game there is no way it could be done anyway).
And as a sidenote don't get me wrong, replayability and lenght of the game are two very different concepts.