I'm not expecting Marshmallow to roll out to my device at all, and nobody that I know who use cheap android device does.
Honestly, the features of the OS are not worth upgrading. The only thing that suffer is my gaming abilities. I can't play the most recent games on it... I guess. I don't game on my device.
Average Android user don't care if they are not cutting edge. They would be using Apple product if they cared about that at all. The only exception are those users that purchase the high-end products. Those will gladly trade their phones to stay up to date, they are the ones in the statistics that keep up with the latest versions. The average user are using Android because it's "the cheap smartphone".
I will move up the chain if main features start to break. So far, browsers, social media networks and all those things have been backward compatible. When they won't, I'll trade in my phone, pay $50 and get another low budget Android phone.