My Harbinger server characters got THORN Hero this morning.
Strongholds were introduced for subscribers. If you subscribed when they first announced strongholds all your characters can unlock a free Sky Palace on Nar Shaddaa, with 5 extra rooms already opened. You can let one other player (at a time) visit.
Xonanan, my sith inquisitor bought an apartment on Dromund Kass. The apartment is only 5k, but will cost nearly 2m to unlock all the rooms. Which it turns out is a lot less than the rooms in Nar Shaddaa cost. Xonanan opened garage and first couple rooms upstairs.
You get trophies for achievements and since I can't recall which characters earned which I just put them all in every home. You get multiple copies in the form of pictures to hang on the walls.
Each character you do the strong hold quest on unlocks more items. All the same for each but they're unlocked for the legacy so even if you dont want to decorate every characters home you could still do the quest then use the extra items on just one stronghold, which is probably what I'll do.
There's a new operation and new quests I haven't tried yet which reward stuff for strongholds.
Strongholds are legacy bound so when you unlock Nar Shadaa home its unlocked for all your characters on the same server. Each character that you take to it though counts for the quest. Unfortunantly there is a limit on how many companions, pets and mounts you can display. So no way to show them all

Same is true for Tatooine which is also a neutral planet.
The alliance capital worlds of course only unlock for characters matching the side.
So home on NS has only Josra's companions on display, including HK-%1 but not Treek.
Home on DK has Xoanan's companions including Treek on display.
I may never own Tatootine home its 2.5 million just to unlock basic home.