Undertaker is more open to working more shows for WWE this year, according to the recent Wrestling Observer newsletter. More so than the past several years. As previously noted, he is scheduled to work on WWE's tour of Mexico. He is not advertised for the upcoming tour of Europe but with John Cena not being on the tour I wouldn't be shocked if they asked Taker if he could appear on those shows.
Taker is said to be in better shape physically because he's fully healed from surgeries and injuries. He may work some shows here and there before WrestleMania. Of course, he's booked to wrestle Brock Lesnar at Hell in a Cell.
Also, for anyone still wondering, there is no talk in the direction of a Sting vs. Undertaker match. It seemed like The Undertaker's last match would be at WrestleMania 32 but Jim Ross noted on his podcast that it doesn't look like Taker is ready to retire just yet.
Also, in a recent Q&A on his website, Ross said, "I could see Taker working a part-time schedule similar to Lesnar’s until his health won’t permit it but it seems as if the Deadman is in great shape at this time."