1) It's perfectly okay (and good) that GNU maintainers do not want to have features that are needlessly exclusive to a given platform.
2) It's perfectly okay (and good) that they want their software to behave consistently across platforms, as otherwise those are not really cross-platform.
3) Coloured typeface are illogical, just use pictures, which is what emoji are. It's fairly easy to insert images into a buffer in Emacs.