Roman Reigns vs. The Undertaker is still being planned as one of the WrestleMania 33 main events, according to the Wrestling Observer Newsletter.
Even after Taker was in pain following the Royal Rumble, and despite the fact that the crowd's reaction to Roman Reigns will likely set a record for loudest booing, this has been a pet project of Vince McMahon's for quite a while. It is thought this might be the last chance since Taker's failing health might lead him to retirement sooner rather than later.
Reigns eliminated Taker in this year's Royal Rumble match, mean-mugging him afterwards and telling him "It's my yard now." This was all to set up a beef for a WrestleMania feud. However, The Wrestling Observer Newsletter is quick to point out that Vince's plans haven't changed: make Reigns the face of the company for the long term future. To that end, many believe that this feud would lead to a generational passing of the torch, even though a receptive crowd would be unlikely, as unpopular as Reigns has become with a large section of the fanbase. Don't count on an official heel turn, though.
As far as Taker's health goes, he had hip surgery last fall but still needs a full hip replacement, something he's been loathe to do until his in-ring career is over.