Assuming we straight out kill Garrosh in SoO, there ought to be a memorial for him or the deed afterwards. Lich King had the statue in Dalaran, Deathwing's jaw was split between Stormwind and Orgrimmar. What about Hellscream? I assume Gorehowl will be re-introduced as a more powerful 2h axe than the Kara-equivalent, so that won't likely be part of the memorial. Or could it..? Perhaps a statue would do.
I've long wondered what the purpose for this empty space is. Now I think it's a fitting place for something for us to remember Garrosh by, if Thrall/the new Warchief chooses to honor his memory that much.
As for Stormwind.. I dunno, maybe somewhere in the palace?