Ah, for the days of old, when you could just ask nicely at the counter for exit row...

This isn't totally dead. I missed a flight last year and got bumped to a flight the next morning on some weird ticket class where I didn't get a seat assignment until the gate. The gate agent was able to give me a bulkhead seat with extra legroom at no cost. And this was with United, not some airline with a shining reputation for customer service.

So you can roll the dice and try to get a premium seat at the gate, but that's not a risk I'm usually willing to take.