I'm off two minds about this. Implementing lvl 5 could be a very time consuming effort and every addition to EA is likely to add time onto the final release. Most classes wouldn't be that hard, since multiattack is already in the game and increasing Sneak Attack damage from 2d6 to 3d6 can't be that hard once they've figured out going from 1d6 to 2d6. But 3rd level spells are a whole other monster. That's a whole lot of animations and effects that need to be programmed and playtested enough to work in EA.
On the other hand, lvl 5 is the first major powerbump for most characters and it seems likely that we will be lvl 5, or just shy of it, when we first enter the final couple of areas of the EA. These areas also feel like they weren't designed for lvl 4 characters. Giving us the option to reach lvl 5 would probably give them a lot of useful data for tuning the difficulty of these areas. If they collect data for the Grymforge and Underdark for lvl 4 characters and tune these areas accordingly, but most people reach lvl 5 by then, the difficulty curve will be all over the place. Which is definitely my impression of the Original Sin games.
