That’s quite an old topic quoted there eh.
Z-index / overlapping regions will work on android client only (for now).
It will be our goal to make this work as well on our new cross-platform player, which will be developed for 1.9 series - Cross Platform Player Specification
Since we just released 1.8rc1 and still are working on 1.8 series, we can’t commit to any solid date regarding 1.9 or this new player.