I for one really welcome the inclusion of the Model T (and Life Pedal for that matter too). The Model T may have been around in the 70s but it really only rose to prominence in the last 20 years (the prices they fetch nowadays are obscene to be honest, and they're getting very hard to find) within the doom metal scene, as they were extensively used by Sunn O))) (a band that literally named itself after their favorite amp brand). It's basically a holy grail amp within that scene, on account of it's insane headroom and bass/lower mids. A lot people want that kind of sound, but they can't exactly afford to spend in excess of 5k for a 50 year old amp.
Now most modelers cater to classic rock, clean, blues or modern high gain sounds. It's kind of rare to see anything catering to the doom crowd, but it's great to see that Line6 is making an effort to reach out to that crowd too that has so far been largely ignored (though I suppose it's a mutual thing as a lot of doom metal guitarists seem to be very preoccupied with analog gear). Ever since Metallurgy Doom was released I had hope that the Moo)))n would come to Helix too - the fact that they added the Vital Distortion (another coveted piece of doom gear) is just the icing on the cake. I could see a lot of doom folks looking into Helix on account of these effects (as well as the two Oranges, which are already great amps).
It's not exactly as popular an amp as a Fender Twin or some kind of 5150 but Line6 is wise to branch out, as those bases have already been covered extensively by them (as well as their competition) by offering something actually new and novel. As far as I know the only other modeler that offers some kind of Model T emulation is the Quad Cortex, and I don't know if that one can replicate the jumped channel sound that most people use with the amp.