Not sure how long Panasonic will produce Plasmas, heck I am not totally sure even Panasonic knows as of now. It will probably depend on whether they are meeting their sales targets or not. At any point they may stop or extremely limit production, especially if sales are not there, which they don't seem to be on the VT/ZT. The ST's seem to be selling really well though.
The Panasonic Insider has said they will produce 2014 Plasma's but will not say what the line will consist of. My thought is there may not be a ZT, but definitely a S, ST and most likely a VT. They seem to be transitioning their LED's into playing a bigger role in their TV line. I have read that they plan to announce their 4K LED's at IFA in Sept. My guess is that they hope the increased income from the 4K's and increased LED production will tide them over until OLED can become more of a money maker. The only problem with this is that their current LED's are not that good. If no one is paying attention to your LED's how can you just jump in the market and hope to be a major player in 4K LED's ?
Sharp Elite 70X5FD
Pioneer Elite SC-07, SC-05 Receivers
Martin Logan Ascents
Rotel RMB 985MKII
NHT VT-2.4 Surround System
Velodyne DD-18 Pair