4Game

As the title says really, I thought it was pretty cool when they allowed you to switch the nationality of the Rudy but as far as I know that's the only switchable tank in the game.

Has there been any news or announcements of tanks that could get it in the future?

I figure tanks like the Tiger II C could be American/German (German made, captured by Americans)

The 59 Patton could be American/Chinese (Mashup of American and Chinese vehicles which I don't think ever actually existed)

Then there's all the low tier captured French/German stuff (French made, captured and modified by the Germans)

The two variations of the Tiger I could be cross nation as well with 131 being German/British and the Type 6 bring German/Japanese (Both German made, one captured by Britain and one made by designs sold to Japan)

A bunch of American and British vehicles could be cross nation due to the lend-lease program between the US and the USSR. This would include;
Matilda II
Valentine
Sherman's
Churchill
The almighty M3 Lee

I think it'd be a good idea to restrict it to premium or reward tanks to stop tech trees becoming a complete mess of cross nation tanks but it'd be nice to see more cross nation vehicles in game.