The main purpose of early access is to make it a 'must have' to get almost everyone pre-ordering. The pre-order numbers gives SE a rough guide for how many people might be coming back to the game for the expansion and they can prepare accordingly for those numbers on the 19th. It's a clever move as they won't get surprised by a surge of people buying that did not pre-order since the only way into EA is via pre-order.

There'll be a small additional spike on the 23rd but nothing compared to the 19th.

Quote Originally Posted by Kit-Kat View Post
Iirc, new tomestone will be released 2 weeks after launch, together with Alexander.
It is only Esoterics that will be released later. Law will be released with the expansion.