According to the Las Vegas Sun Katy Perry has been offered a sort of mini-residency in the AXIS theater where Britney performs PIECE OF ME.
The show would take place during Britney's hiatus between the 100 shows (i.e May-August); the news comes after Katy performed for a group of execs/high rollers during the NYE weekend
Source: http://www.lasvegassun.com/vegasdeluxe/2014/jan/02/strip-scribbles-katy-perry-following-britney-spear/
This might not be completely Britney related but it goes to show that Britney is still impacting the music industry - she made history with her residency and despite many people doubting her legacy, she's setting a new trend and receiving amazing reviews at the same time!
I don't think Katy's show would be as successful as Britney's - she doesn't have the catalog for it or the stage presence to carry a residency.