I'm not exactly sure what you mean by this. Do you mean consumers will use/buy older Android devices for very specific tasks?
I think the exact opposite of this will happen. Your average consumer is not going to want to have multiple devices. They just want to carry their phone around and have it do everything for them.
Your microwave currently has a home-rolled LCD+pushbutton interface. Within a few years it will be an Android powered touch device. Probably out of date before you buy it with no way to update.
But who cares, right? It's a microwave. As long as it still performs its microwave controlling functions, it doesn't matter if top new Google Play apps don't run on it.
I'm not 100% sure how realistic this is. But I have a feeling it's close.
Your "average consumer" already does. The point is that Android in three years will be serving an even wider range of devices and household appliances.
While I agree a lot more devices will be running a more complicated OS with increased capabilities in the I future I don't think it is a foregone conclusion that it will run Android. Android is primarily used on phones, tablets and TVs because of explicit design choices made. Perhaps they will position themselves as a generic OS for electronic devices but they have some work to do before that can happen.