We'll know far more in the second week of January - 7th January sees the start of the huge Consumer Electronics Show, which is the traditional venue for all the big manufacturers to preview their wares for the coming year.
What Hi-fi? Sound and Vision will be there, reporting back here on all the new announcements, including as much information as possible about UK release dates and likely pricing.
On the specific Panasonic front, I also know they're planning a huge dealer event in early February, when they'll show all the new 2008 products for Europe. That suggests a March-onwards roll-out...
With it being European Football Championship year (don't mention it!), i'd expect all the major manufacturers to have their new TVs in the shops by May at the very latest, to deal with the usual up-lift in sales a summer-of-sport causes.