Why would you? Just for the 15k TY point bonus? I guess since the 15k TY points count for flight points matching...

AFAIK, they don't waive the annual fee for the first year on Premier Pass Elite, so I think for simplicity sake I would keep my PP and churn another TY card - its pretty easy to find TY cards that give you 10k bonus (Professional, Diamond, etc), but you can't use these for flight point matching. You can, however, throw them in the same TY account so you can use them as points to get flights with. The CitiBusiness TY card gives you 15k bonus points of you apply through the right link, but unless you really have a business I wouldn't churn this as it may look suspicious if you apply as a sole propitiator every time.

Note that Citi only allows you to apply for 2 cards within a 90 day period, and I've read they are strict on allowing you to get too many of their cards (3-5 max, but this isn't an exact limit, some people have gotten higher). Citi Personal and Citi Business are separate though.