I've read over the playtest stuff a little more. There are a couple of things dealing with Hit Dice that caught my eye. It may be due to the incompleteness of the document, in fact I am sure one of these quibbles is a first-release oversight. Even so, they raise some questions about the direction of the rules concerning Hit Dice, hit points, and healing.
First off, hit points. This one is short and sweet. The rules state that beginning hit points are equal to CON + CON modifier. Survivability boost. I get it. It then goes on to say that when a character gains a level, roll the appropriate HD and add it to the total. If the roll is less than the CON modifier, add the modifier instead (emphasis mine). So, CON mods aren't added to hp after 1st level?
Then, under Resting, it mentions that during a Short Rest a character may be treated using a healer's kit. Each such treatment allows the character to expend one HD. Each HD expended is basically rolled like a, well, like a hit die, and deducted from the character's damage. I can't find any other mention of "expending hit dice" outside the section on Resting, so I'm unclear about the overall effects. It seems like it is just a limiter on non-magical healing. Sort of a reskinning of the Healing Surges, just less potent. More info on it would help.
Oh, one more thing. Also under Resting, it states that after a Long Rest (8 hours) all damage is healed. You do have to have at least one hit point to take a long rest, so if you're at 0 you won't wake up feeling any better.