We need to hold the line somewhere. Preferably before corporate logos get into Unicode. I've seen Facebook and Twitter icons as Unicode characters in the user-definable space. This currently requires a downloaded font, but there's probably some lobbyist somewhere trying to get them into Unicode.
It's getting really complicated. There are now skin-tone modifiers for emoji.
Unicode is turning into a few useful characters amid a sea of junk. This will continue as long as people acquire status by getting "their" symbol(s) into Unicode. I don't see any way this can change.
How are Windows and Java, which are somewhat tied to 16-bit Unicode, handling this? It used to be that the astral planes didn't matter much, but now they do.
That's what surrogate pairs are for. [1] You're no longer working with one code point per character, but even with 32-bit Unicode there's no real guarantee of that (consider things like combining characters, accents, emoji skin tones, etc.)
Unicode is 21 bits wide. And there's lots of space left. Heck, Emoji still make up very little of the total encoded characters, compared to “normal” human writing systems. (And I'd argue that emoji are by now a normal addition to writing, considering how many people use them daily and can be glad to have them interoperable across different platforms, carriers, and devices. Something that hasn't been that way previously.)
It's getting really complicated. There are now skin-tone modifiers for emoji.