Probably making it optional keybinding would not hurt as well as something like "last used emote".
And what about making emotes accessible via quick chat, like "/e o7"?
The part with the "/e o7" sounds oki. According to standard in other emotes, it would even be merely /o7.
Having it as text to trigger has the big advantage that you can have plenty of them and are able to trigger them quickly when you want to. Of course, we'd also need to have a list-like menu available. It sure is a slower way to get to them, but as you probably don't know them all by heart, especially right away, this feature would absolutely be needed. And would be easier to expand than the wheel they show.
On optional keybinding: but which ones would be worthy to be a bound key and which ones not? How many would you bind? And could i have the Shutdown Field Neutralizer as emote, please? That one is begging to for a hotkey since many years and still got none.
I also see some need in a tool, which can mark certain targets and optionally share their positions with your teammates. Or even some sort of tactical map tool for quick navigation in combat zones and coordinating team actions (so to mark positions on battlefield), but that's another story...
That's a good thing. But not an emote.
