My prediction is that digital will begin to flatten out. My son's point and shoot makes a 16 MB file every time we make a snapshot. It's ridiculous! Every time we turn around we've got 4GB of movies and snapshots!
I usually shoot on a Canon 5D, but I rented a 5D Mark II last year for a large commercial job. In 16 bit, with a few layers, the files were so huge that I could barely handle them on my not very old Mac.
The two big medium format digital companies, Leaf and Phase One, have now merged into one unit, with the Leaf backs being rebranded for Mamiya. Seriously sexy stuff, if you can afford it, but not many people can, nor find it necessary, which is why the companies merged. The local rep called me with refurb Leaf 22MP backs on sale for $4K. (Very tempting, but I'd probably only use it for my personal work.
Like you said, the hardware couldn't support the digital cameras for a long time. I think we are moving in that direction again, only this time it's "How Much Data Do I Really Need?" cause these 24MP files are making my computer crawl!
The 5D files are beautiful at 20x30 and larger. A good RIP can take a 10" file and make it a flawless 30" print, no problem. More mega pixels means longer downloads, more storage needed, faster computers, faster internet, etc.
So, I've avoided upgrading for these very reasons, as have others. My first book was shot on the 5D and looked fantastic - what more do I need?