They're supposed to merge them in 4.1, which will be soon.
PTR hasn't changed much, at least to my knowledge -- maybe it has and I'm oblivious, but don't recall seeing much new in a while.

The whole idea of press and release.
If you're off of the GCD, and the step 1 ability is available (runes/runic power/cooldown/whatever) it will fire off.
So we have Mind Freeze on step 1.
And either Howling Blast or Obliterate, as those are primary abilities for those two spam buttons/rotations.

Then have a bunch of stuff on the second step.
Which can be on release.
But it could also be on press, and then every other step is the stuff on Step 1 or the stuff on Step 2.
Honestly, it won't make a difference in the game.
In the one case (press and release) you spam at whatever pace.
In the other case (release only) you spam twice as fast for the same result.