I'm using the latest Zathras with 3.6.14 build for quite some time, and it basically works. Of course debug builds complain about this and that, because let's be honest, the tables are a bit of a mess.
The way it is now with 3.4b and Zathras on top of it, there are too many tables/modular tables overriding each other. And there's a lot of table entries which were added originally to make BHX work, but now just clutter up everything.
If you want my opinion, in the long run there's no way around condensing everything into a clean base again (basically TBP 4.0), especially if we want to use all the fancy new features that require table and POF changes. Which also eventually means breaking backwards compatibility with existing campaigns.