Part of the advantage of Newtonmass is that it's a sufficiently clever joke (IMO anyway) that it becomes less about sending up Christmas than the double meaning of "mass." Or at least it can, if you explain it right.

Regardless, I don't think either Baconmas or Newtonmas or Newtonmass are actually all that offensive. My suspicion is that the sort of Christian who would get annoyed would also be annoyed at the range of politically correct holiday greetings that explicitly AVOID mentioning Christmas at all, so the reference builds Christmas' importance rather than diminishes, in some ways. Dunno. I don't know if I have a good enough model of the type of people we're concerned about here.

However, an alternative: Baconalia