For that matter, even a standard RGB map should work for stacking BOTH of the features into. If you only need 2 channels for the Team Colors and 1 channel for the Gloss, combining those into a -TAP map for explicitly those features might be a better way to go. I woud not want to imagine Gloss maps with an Animated Glow map, for example. You'd have to alter the alpha on all of files in the sequence.
Okay, it probably doesn't need to be called a -TAP map, but you get the idea I hope. And lets take it one further. make it an RGBA map and add an Anisotropic control channel in there as well. 1 additional model map, covers 3 functions, doesn't interfere with the utilization of existing maps (or compromise quality for using them in an alternative fashion) AND makes it extensible for use -outside- of the given mod without requiring rejiggering any assets to any other mod that may choose to adopt the option. Like, Starfuries in TBP, HOL ships in FS1/Reconstruction, X-Wing Wings in Fate of the Galaxy, etc.
Yes, we -do- have two unused channels in the normal map and at some point it might be nice to correct that, though if a 3dc/bc5 is the same size as a DXT5, might as well stick to DXT5_NM. Yes, we do have an alpha channel on the diffuse and the glow maps (and they actually DO affect the maps when not otherwise told to do so). Yes, they -could- be re-purposed into providing extended functionality, but it hampers adoption by others that may be interested in doing so by -requiring- all previous maps to be either redone, or potentially introduce quality loss by editing and re-saving them to do so. Or introduces garbage if/when somebody introduces an asset to an adoption system that isn't made to utilize that feature, which is why Anisotropic Reflection isn't using the 2 "unused" channels in a normal map either and I'd hate to see what would happen if somebody inadvertently tried to do both AR and Team Colors at the same time.
I do get that we want to limit how many extra files we add to the stack of being loaded per model. We don't need to arbitrarily or unnecessarily raise that count. But I don't think the answer should be shoehorning functions into areas where they will either A: produce quality concerns (whether or not you or your mod share them or think them of consequence or worse, can only be over come at cost to the end user experience) or B: produce significant adjustment issues towards adopting them.
So in this case, I'd really like to heavily recommend that we DO actually add that "one more map" to the list and collaborate on the most effective manner towards implementing it (How many channels should it be, which channel is going to handle what, etc) and make this something that is fit and easily used and usable by everybody.
Mind you, that's just my two cents and I only make it as a recommendation, not as a discouragement.