Instead of selecting text I'd rather have a dedicated softkey to emojify what I type after. E.g. ⁂poop spits out pile of poo emoji. Tap and hold the button and the emoji menus show up.
HipChat uses parens for this, with (thumbsup) turning into a thumbs up icon even if you're communicating through the IRC bridge. It's a bit weird when you're using parentheses for a parenthetical and it pops up the emoticon search, but you get used to it.
The Slack equivalent, which wraps the keyword with colons, :+1: is less likely to happen on accident. I am surprised HipChat went with parentheses, honestly, but maybe they felt they were too subtle for mobile users (I like them, myself). It is nice to have a text-only method of mapping to emoji, though.