how can you expect evidence of something that has not yet happened? That article is about how to keep things clear and understandable now. Nobody there said language is going to hell altogether.
People have been saying language is going to hell altogether for at least 400 years. Also, languages don't go through these changes at a constant rate. We can pretty much understand Shakespeare with minimal help from notes, mostly about word meanings but check these samples:
Geğenc hwelc witu us ğa becomon for ğisse worulde, ğa ğa we hit nohwæğer ne selfe ne lufodon ne eac oğrum monnum ne lefdon!
compared with
This frere bosteth that he knoweth helle,
And God it woot, that it is litel wonder;
Freres and feendes been but lyte asonder.
And grammatical correctness is not a guarantee of understandability. Here's a headline from BBC News:
Escaped wallaby caught using huge fishing netSure, it could be worded differently, but there's nothing grammatically wrong with it.
