Given Triumph's model track record, the logical next step for the T-bird will likely be a 'blacked out' version (to be named, but I like 'Blackbird') to compliment the T-bird as the Speedmaster compliments the America, and as the Rocket Touring compliments the Rocket III. This makes sense to me, since production costs would be minimized while introducing a bike which appeals to a different segment in the same market and keeps the 'buzz' for Triumph as a brand in the trade news as a marketing tool.
This will all depend on how successful the T-bird is in the showrooms, among riders, and on the balance sheet. I predict that this wil happen within two years as long as the current motorcycle market remains robust.