I do believe that they'll stick with the Fathom name, just with another sub-name included.
I'm almost certain that it wont be called Fathom. Fathom is a unit of measurement that is almost always used in context with water.
'Heat' as Ellusionist calls the teaser pictures, is probably too bland and simple. I'm sure they'll eventually come up with some sophisticated word to represent the fire theme. Blaze, Inferno, Ember, Luminosity, Pyre, Flare, Radiate, Ferocity, Vehemence and Frenzy are my best guesses/only words in my vocabulary that i can associate with fire =p
Of your guesses, only Blaze, Inferno, Pyre, Flare and Radiate more directly connect to fire. Luminosity applies to light more than fire, while Ferocity, Vehemence and Frenzy are more like animal or human traits/actions, all implying at least a minimal level of intelligence or instinct which fire lacks. We use them occasionally to describe fires, especially destructive ones, because people will often anthropomorphize "the boogeyman" or anything they fear, particularly forces of nature. Those terms could as easily be applied to a wild tiger or gorilla.
The thing I can definitely agree with is that this deck will not have the name "Fathom" on it. Fathom has absolutely nothing to do with fire - it's usually either a measure of water depth or a synonym of "understand." When Fathom was released, they stated that they'd be making a deck for each of the four elements. After the "fire deck", we still have earth and wind to look forward to. I'm already picturing the ad photos on the deck's page at E - who wants to bet they show cards on fire, actually burning?
