^I think there definitely will be. Or definitely should be, to 8GB of RAM, at least.
I love the idea of a Mac Mini for my parents, but my only problem is it's a desktop with a lifespan of a notebook (three years with an extended warranty). Meanwhile, their 6-year old small-form factor HP desktop has had literally every part on it die at one point or the other, and since it's been out of warranty, outside of Mobo and CPU, I have slowly been replacing each dying part with a part that would be right at home on a high-end workstation/gaming rig.
I would love to get them on OS X, or Windows 8.1, but I'm worried that 8.1 is going to be too much of a change for them, and it would be nice to get them completely into the Apple ecosystem, especially for things like iPhoto, Contacts, etc.
Not sure where you're getting a three year lifespan. If all your parents do is surf the web or word process/account/productivity any computer you buy now will last a lot longer than three years.
I used to go by the adage of buying a completely new machine every four years because that's what the business demanded but these days I'm still doing billable work on an old 2008 Mac Pro and it's quite snappy still.