Technologies have come a long way, I don't think you can extrapolate the first couple of years into the future, ad infinitum. There's always going to be a spike in advancement in the early stages which may result in loss of compatibility. Everyone is far too invested for half the data in the world to suddenly become unreadable (obviously not just photographers and photos, but it's all the same).
I'm not convinced about the whole thing anyway. I'm sure if you really wanted to, you could get at pretty much any digital photograph regardless of when it was taken.
On the other hand, a print isn't just a print as I'm sure you're aware. Quality varies massively. And the life of a print is dependent on any number of factors, from the quality of the paper and/or the inks, the quality of the glass and the framing, the conditions it's kept in... to being dropped when they move house.
Think I might be mis-reading this, but are you suggesting that photographers are the anomaly in digital storage capabilities? ie a 'normal' household has the ability to archive the files, but a photographer doesn't?
EDIT: Is there a 'don't' missing from your OP?
Why? Just an assumption about future compatibility?