Here's my feelings about it after respeccing a few characters I transferred over to the test server and building some fresh ones as well.
1) This adds a lot of freedom to builds without putting any major changes on level 50 outcomes. The number of slots at low levels will act as a good check on overburdening a build with high tier powers. As a solo-heavy player, I'm really looking forward to playing tanks again, which normally are a chore to level up. My Defenders and Dominators will probably all be losing a T1 power hooray!
2) This new freedom also makes it easier to make terrible builds if you're a new or casual player. The prior structure encouraged a natural distribution of slots and end over the the rise from 1-40 with power pools stretching out the time before slots would start going to new higher tier powers. That's gone now. There are going to be some people who build terribly and conclude that "XYZ powerset sucks". Not a big deal, but a problem if you want to expand or keep your current player base.
3) This change makes the current exemplar system seem way OP. Time to take the +5 off. It'll be good for the high 40's TF's too, less incarnate powers, more basic high-level heroes.
4) This lays bare a totally separate problem: A lot of T1 powers are just garbage and that's no fun. Blasters get a special consolation prize for having mostly worthless T1 secondaries with Defiance, but the fact of the matter is that this suggests maybe rather than having a system that lets us consistently avoid a power selection, maybe we should revisit the T1 powers instead?