I think it has already.

My feed now looks like this:

What should a 22 year old do with $3000

What should a 23 year old do with $2000

What should a 25 year old do with $5000

on and on and on.

A few years ago, it would have been "How can/should spending and saving evolve over a person's life?"

I know that's a specific and perhaps pedantic example, but there's been a definite shift in the vibe on Quora, from a place where users hoped to contribute insight, to a place where users feel entitled to receive it.

Agreed. Killed the e-mails with toplists from Quora some time ago. Too much bs.

I also think it has happened already: I want to search for questions about the big bang, I'm typing lazily, expecting the system to auto complete my intent; but when I am at "big b", the suggestions are: "big brother", "big breasts", and "big booty".

The kinds of conversations I have seen on Quora and arguments about god and other things have led me to believe it's already kind of overrun with silliness.

that is a very fair statement