'As and when they are released' Android added Now TV like 2 months ago, Apple TV about the same, UKTV Player, CBS and Horror channel catch up last summer summer BT TV got added in the summer aswell. These apps have been available for years and even Google have only just added them.
You can only really say Samsung are good at getting Apps fast.
I just don't think Panasonic are looking to add the 1000+ apps you get developed on Android/Google TV if it sacrifices the ease of use. Not to mention you have to hand over complete control to Google. I can just picture Sony sitting in a room royally passed off because they have built Amazing TVs yet are getting slated in reviews and having TV after TV returned because of how bad Android TV has been in the past
. (Sony of course had very little control over updates)
If Google TV gets better reviews than android TV did I don't see why Panasonic wouldn't adopt it but I think Panasonic would want to see it be recieved & reviewed positively first.
I'm sure Panasonic are looking to add Disney+, Apple TV etc (the major ones). And hopefully they do.