First, using Titanium will always be supported in EQEmu, so you don't have to worry about that. There are definitely advantages to using newer clients, but Titanium is fully playable and always will be. See this Wiki page for some of the features on newer clients:
http://www.eqemulator.net/wiki/wikka...ClientFeatures
As for HoT, there isn't really anything explaining it yet. It basically means you are playing with a fully patched to Live client. We are not really keeping up on patches from Live for HoT, so you may or may not be able to even fully log into a zone with it. Even though there is a patch file for it, we definitely are no where near fully compatible with it so it would basically be unplayable compared to any of the fully supported EQEmu clients as seen on this list:
http://www.eqemulator.net/wiki/wikka...ClientVersions
Basically the state of HoT will probably remain as it is now until SOE releases their next expansion and updates the client version on Steam. Otherwise, we will be fighting with Live each patch they do to make sure the server is updated and compatible. Once there is a static download from Steam, we can be pretty sure that it won't change again for another year which makes putting work into it much more worth-while. It will be a considerable amount of work to get it fully functional, but once we have the new client that will be used for EQEmu, it shouldn't take long to get HoT 95% or so caught up with the other clients and the last 5% may take a while but will probably be worked out over time.