When new keywords have been introduced into the rules reference, they usually showed up on unit cards that were released more or less consecutive.
There are allready two units with "Wookiee Trooper", but the keyword does not have any effect yet.
It may be that it was introduced for some GAR unit we will see later next year, but I'd say that would be less likely than it being connected to the second rebel unit that will come with Lando (Lobot might be another obvious choice, of course).
So what could it be?
Another generic or named character with "Direct Wookiee Trooper"?
A Raddaugh Gnasp fluttercraft?
An Oevvaor Jet Catamaran as a transport for Wookietroopers (maybe a little bit too long)?
Another brand of Wookiee Warriors with other weapons and upgrades thar are exclusive to Wookieetroopers?