HoT Access, re: Living Story
You don’t have to play the LS to gain access to Dry Top or Silverwastes.
It would be stupid if you would have to buy the LS-Chapters and play them to access content you already bought. Lvl 80 should be the only requirement.
I imagine the entrance to the Heart of Maguuma areas will indeed be in either the Silverwastes or Dry Top (or perhaps both, as there are areas in both that could conceivably connect to other areas).
However, access to those areas has nothing to do with LS. You can go to them on any character without ever touching the LS chapters at all. The LS just pseudo-guides you through them (moreso Dry Top), but you can go there any time regardless. So I don’t forsee any problem there. It’ll be no different than, say, not being able to get to Fireheart Rise without first going through Blazeridge Steps.
You should probably open up those areas on each character just for ease of access to HoT content, but you shouldn’t need to do anything with LS if you don’t want to.
Since people can buy HoT after the current Living Story stops being available for free, I’d imagine that it would make zero sense to require finishing the LS to play HoT.
Also, there’s a precedent: you don’t need to finish the Personal Story to play the Living Story, despite LS taking place after the PS and references to the PS in the LS.