This doesn't really address the core of the issue, but it's not a bad start to the thought process. "Tucking the mechanics in" robs PC's of some choice, makes balance a bit wonky, and, as Mearls points out, ups the DM bookkeeping. It's not a good fit with 4e as it exists.
It could be a great way to ground-up a new combat system. FFZ isn't much different -- the players are given an attack, damage, and any keywords or statuses (along with the cost for using the ability).
So much in 4e relies on different kinds and types of movement to balance it and also for strategic variety that just "making the DM handle it" isn't a satisfying solution. But it's interesting that Mearls is thinking about it. Maybe they're tossing around ideas to lower the barriers of entry to D&D (which, in 4e, consists of a significant investment in little plastic toys and accessories to play), which could be cool.