It's a beta-server specific thing, but it's not handled by devs/gms - it's built into Beta's systems. The minute you hit 50, your alpha slot unlocks, even if you're non-VIP (with a friendly message from Black Scorpion, to boot!)
However, I'll admit it's a bit nitpicky on my part to mention it. Even though you can unlock the Alpha slot on beta, create a power, and slot it in, it has no effect. You'll see it appear among your automatic buffs for a split second, then it cancels. Only VIPs get to actually use incarnate powers.