Honestly, I don't know how far along the game is. Game development isn't easy and Rare have a history of throwing out many concepts which never see the light of day.
A good example is Kinect Sports Rivals. Originally Rare had MUCH BIGGER plans for the game and it was supposed to take place on an island that you could freely explore or something. Well, at least that's how my brain remembers it.
Anyway, one thing lead to another and that's why we got that shitty watered down Kinect Sports Rivals. I think Lionhead Studios even had to step in to get that thing finished and rushed out the door.
Back to Battletoads. Ermm, an educated guess on my end would be that we see a full Sea of Thieves reveal at E3 alongside a Battletoads announcement. Perhaps maybe just a teaser depending how far along the game may or may not be.
Don't worry about Battletoads too much. Keep an eye out for Sea of Thieves. Rare's love for all things pirates can be traced back to Donkey Kong Country 2 and Sea of Thieves is probably Gregg Mayles' dream game.