While I wouldnt mind having one of each model cost wise Its a bit prohibitive so I've been looking at an alternative that would allow me to use the same model as either a Frostheart or Flamespyre Phoenix.
Paint it with Blue/Orange Flames similar to the pictures below.
If I can get this right then I don't see any issue with fielding a single model as either the Frost or Flame version. Blue Flames are still Flames and in fact are (for some scientific reason) actually hotter than orange/red ones. Going to start it this week with the aim of getting it ready for Skitterleap in October (or possibly Warpfire in September)