#4 The Undertaker could manage a wrestling faction
It's hard to imagine The Undertaker as a manager in WWE. There are very few wrestlers that he would not overshadow, were he to accompany them out to the ring.
In this role, however, The Undertaker could help to lend credence to a number of wrestlers instead. If The Undertaker managed a wrestling faction as the mind behind their operations, he could easily help to build the careers of several wrestlers.
For example, MVP in The Hurt Business hardly needs to wrestle now. AEW's Team Taz does not need Taz to wrestle either. Similarly, The Undertaker could simply be the face of a faction, and help build several other wrestlers' careers in WWE.
A sinister faction, where The Undertaker is shown as the mind behind their chaos, could easily lead to some extremely entertaining storylines in WWE. Simply through association with The Undertaker, the wrestlers in the faction would be pushed to new heights.
The Undertaker would just need to be a manager and cut promos. Thus, he could also help add something very fresh to WWE programming.