There are a couple or ways the fiat - bitcoin thing can completely break.

1. bitcoiners decide not to deal with fiat ever again. (total dream)
2. Fiat is really dying, and people can see it coming
3. Bitcoin value is going up so fast everyone is waiting to sell.
4. So much fiat per bitcoin that one cannot move enough fiat into an exchange to trade for an amount that is transferable.

And i am waiting for guys in trenchcoats to stand around streetcorners trading satoshis for dollars.

A lot of the altcoins are not going to make it. Most won't. Like 90% won't.
I just don't know if it is all going to be bitcoin. Bitcoin maxis make a good point.
However, there are tokens that are important for their function.
And there are coins that will probably fill the gap between bitcoin high and slow, and the normal transaction.