I would guess multiclassing will only come in a later stage in the EA. I would assume them to first want to see the classes themselves working and being balanced (and working) before they have to worry about combinations. Also multiclassing won't be that interesting when you have such a low level cap.
Actually I'm going to argue that Multiclassing helps to keep it all a bit more interesting.
Multiclassing helps even at low levels when it comes to making most of the races relevant. For example. If you're not picking a class that gets Perception as a skill and you want your character to be the party's Face/Rogue-lite, then you might as well pick Wood Elf (who also gets Perception AND Stealth AND extra movement, all for free) over all of the other classes. Even if you have to wait to fourth level to get another +2 in a primary stat.
Whereas with Multiclassing you can rely on a 1 level dip to gain a better spread of skills for a Face and pick just about any race for more diverse combinations that still net you relevant skills.
This could also be addressed to a lesser degree by adding more backgrounds from supplement books, but I'd much rather play a LVL01 Rogue/LVL03 Warlock, even with the cap at 4, and choose a different race.
