There's plenty in the English language that only makes sense to people on the internet.

I'd like you to imagine, for a moment, how this might evolve over coming centuries. Looking at the trends and memes etc. and the rate at which new networds are absorbed into the official dictionary, what do you think English might look like in 400 years?
Grammar is changing too - many nouns are being verbed and things like lolcats (and a certain dog) have added commonly understood non-grammar phrases to our language. There are shortened phrases that only make sense to netizens.
Put all of this together... would we understand someone speaking 25th-century English? Would we sound to them just as odd as Shakespeare can sound to us?