Though they have pretty much gone under the radar there have been a lot of Legends contracts recently to I would say lesser known legends. Recently Billy Graham, Tatanka, and The Boogeyman have gotten Legends deal recently from the company. With how random these signings were I really can't pick who they could sign next out of all the legends they have at their disposal.
Looking at who they signed allows them to open themselves up to a more wide variety of legends for special appearances when they need someone to make a cameo. The idea that they always use the same legends when they need people to make special appearances. Having the ability to mix up legends who make special appearance would provide a tremendous benefit to WWE as it would make the "normal" legends appearances all the more special.