Topic: What is Steam's early access?
But you don't know the whole picture yet, I think you'll understand better when we have laid all our cards.
OK, this is my take on what early access is on Steam.
Browsing the early access games on steam, there is something in common with all Steam early access games like Kerbal space program, Dayz, Rust, Starbound to name a few even an MMO space game Entropy. All these games have no monthly subscription, you buy it once and it's yours.
Checking out what early access means on Steam here: http://store.steampowered.com/earlyaccessfaq
Something of note:
Is this the same as pre-purchasing a game?
No. Early Access is a full purchase of a playable game. By purchasing, you gain immediate access to download and play the game in its current form and as it evolves up and through 'release'.
As you see here you are purchasing a product to access the game so my guess is Perpetuum will lose the sub for a one time purchase, and this is the only way I think we can get loads more players (edit: as Dev Zoom estimates), I am sure it's a marketing stragedy Valve would advise.
If the game remains Subscription based, it would be the ONLY game with this model in early access on Steam!
/Tinfoil hat off