Go ahead, download the codex preview on iTunes and you will see for yourself- Fire Dragons are getting a 3+ save. Special Rules are rumored as the following

-Ancient doom is apparently a penalty when dealing with Slaanesh demons (good luck seeing those on the table though) and its kind of a fun fluff rule. Supposedly -1ld to Fear tests from Slaanesh demons?

-Battle Focus is apparently the run-shoot and maybe additional run rule? That would give them a nice added mobility to their Melta, especially coming out of a Serpent. Fleet only helps with this rule as Fleet lets you re-roll run move dice.

-Fleet…a great rule for re-rolling run/charge dice. Interesting to see how this rule has changed over the years eh?