The problem with this idea of feature backlog, at least everywhere I've worked, is what you really have is an idea backlog. You have some things people want to build, and maybe a business analyst or product owner has done a first pass. But they're far from the rubber-meets-the-road part where someone needs to write out a detailed spec based on the exact current state of the app/system, and the developers start asking questions as they run into unspecified edge cases--all of which usually means sitting down with the client again over a series of meetings.

AI coding agents help speed up none of that. Meanwhile the developers are either sitting in meetings or working on something else while the product owners hash it out with the client.

And sometimes, after all that, you realize the client can get 95% of what they're asking for if you just tweak some existing feature. Everyone's mostly happy, the app stays less complex.