Well, I would bet it will happen. However, just as with Devil's Playhouse, expect an announcement rather close to release (I think Devil's Playhouse was announced about 2-3 months prior to the first episode releasing). I guess Telltale just doesn't need to hype Sam & Max so much anymore (Since its pretty much guaranteed to sell, provided they keep the quality standards or raise them even higher), so they aren't announcing them a year in advance or so, which tends to happen with other franchises that might need hype to sell (BTTF and Jurassic Park were announced long ago).
In fact, I believe that even in a year, we still won't have seen all 5 games/franchises they just announced released. I'm sure at least one will still be on the "pending" list.