Kane would never agree to one. He claims he's been offered at least a short title reign periodically throughout the years, but rejected nearly all of them because he'd rather put younger talent over.
Also, Undertaker/Kane would be a complete waste of a Wrestlemania match with Taker IMO, given his time is limited and he's already squared off against Kane twice at the event. I think John Cena, story wise, would make the perfect final opponent. Taker's never defeated an A-list sort of top tier main eventer like Cena (people like Michaels and HHH are great talents, but still technically second tier compared to even Cena, let alone Hogan/Austin/Rock) and it's the ideal way to go out.
HBK and HHH are not 2nd tier compared to cena. That's blasphemy.