After TWO MONTHS of teasers. Everyone already knew that the Undertaker was returning well before he physically appeared.
With every Undertaker return, there are always the video packages, the hints, etc. There hasn't been any of that this year. If the Undertaker was returning, the WWE would be encouraging the speculation of it in order to draw ratings, as they have in years past. If he was planning on returning, one would think that we would have already started to see the groundwork being laid for it.
There is a huge difference between being physically in shape and being in "ring shape". You can't get in ring shape by working out, its about working out the ring rust, getting your timing back after taking almost a year off, it's about getting back into rhythm. Two very different things. The most physically fit wrestler in the world, the very definition of physical perfection in a wrestler, could be in absolutely terrible ring shape. Someone like Mick Foley, who is in terrible physical shape, given a month, could probably look like a decent wrestler again, because he is in good ring shape, has his timing down, etc.
If the Undertaker were back in the ring training, there would have been SOMETHING leaked by one of the wrestling newsboards or something by now.
Seriously, if the best they can come up with Taker/HHH part III, what is the incentive for him to return? It's boring, unimaginative, repetitive.
Even with Kane, while probably more appropriate from a storyline angle, has already been done twice before as well. There simply aren't many marquee names for the Undertaker to face that he hasn't already been there, done that with, that aren't already spoken for. Taker/Rock or Taker/Cena would have been phenomenal (pun intended). Neither have gone against the Undertaker at Wrestlemania before, and both are opponents worthy of it. Yet, both are occupied.
What other wrestlers would be able to fit in with the Undertaker, to match the level of perceived quality? Who is both left for him to wrestle, and available for him?
Like I said, I hope the WWE proves me wrong, but all of the signs point to the Undertaker being finished. I don't want him to be done, I would love to see him get the send-off. God knows he deserves one. But, he may not also want it. I have no idea if the idea of a send-off even appeals to him, he might be the kind of guy who is perfectly happy having an unannounced retirement and be content to slowly fade away into the history books.