It probably will not be compatible with 5.0 but there is VERY little info on 5.0. There are plenty of FREE themes in this forum. I'm sure you can find something you like.
Also I am pretty sure the people that charge for themes will work with you on an upgraded version for the new OS.
There should be no need to with 5.0. As stated above, it had been reported that they are working. Now I can 100% confirm that all Plazmic themes i have tried work. And best part is the menu are much fast with little to no lag!!!