If your company isn’t tiny your engineers generally shouldn’t be deciding priority. Unless your company is small enough that the engineers have a clear view of all the priorities of the business all we are capable of is saying “This seems really important to us.” And then that has to be weighed by people who have the bigger picture.

But outside of a very small company to me it’s a bigger crime to waste engineer time with all the meetings necessary to give them that full perspective. When I started at my current company I was the only developer and I worked directly with the CEO and our single marketing person. Back then I helped decide priority. Now the company is too big for that. I don’t have time for all the manager and marketing and business planning meetings to be able to decide priority.

As far as defining features, we can propose them like anybody else but I think I already explained why usually it makes sense for them to come from whoever owns that piece of what you’re doing. But this of course again depends on the structure of your company.