Pretty much anything could be done.
I'd been thinking about a block tree, where you'd have geographically  close miners mining at a low difficulty and low block time, and making their own quick chain. Every, say, 10 blocks, they'd hash their blocks (or 10 blocks in the recent past, to guard against reorgs) and a higher level set of miners would have a slower blockchain embed these hashes. Any number of levels. This would allow (A) faster confirmations on a local level without much more orphans due to the geographical (2) proximity, and (B) the ability to scale the blockchain to very distant regions. Like, you know, the actual moon.
This might or might not be similar to what Ethereum is doing, but it's certainly fun to think about.
 Doesn't work well with I2P
 Well, closeness with a metric based on ping, rather than distances