It's interesting to watch the evolution of written language in action. I expect in 20 years we will routinely see emojis in written English novels and news articles. In 50 years we'll see them in textbooks and scientific journal articles.
I can't be the only one who thinks emoji are a terrible idea. Granted, I also don't think logographic characters are a good idea but at least they have thousands of years of use and agreed upon semantic meaning behind them.
Language is just an encoding for ideas, and emojis are a new compression algorithm. Using a single character, you can now convey certain thoughts and sentiments that you previously needed many more characters to reference or explain.
"So then just explain it!" some might respond. "Why can't people be bothered to spend even a little time to write down what they think?" It's an accessibility issue. People have limited time every day to get their ideas across, and they deserve ways of conveying their ideas concisely. There is precedent for this too -- this is why we have acronyms and new words. "lol" and "minivan" don't have thousands of years of agreed-upon semantic meaning behind them.
A final thought -- whether you think emojis are a terrible idea might not be relevant to whether they should exist. Letting people live their own lives to the fullest is much more important than making sure you, I, a future historian, or any other third party understands what they are saying. But you don't have to worry about not being to understand conversations. Given what you prefer, if someone wants to address you as a target audience, then they probably won't use emojis.
This makes me curious. What things can people talk about with emojis that they can't talk about in a proper language?
But you just did. So what does the emoji add to communication? And how does one get the secret decoder ring for it?
There are plenty of emojis that mean different things in different cultures. Some quite amusing.
— Every human being in recorded history when they hit 35 years old.
I highly doubt this. Common shortcurts (such as "it's" for "it is") and dialect is still absent from serious journals (unless it's the research target, of course) and I'm rather sure emojis will similarly be disregarded.