https://letstalkbitcoin.com/blog/post/l ... -unlimited
There is a great explanation in this podcast on how Bitcoin Unlimited regulates the blocksize.
A node will accept any size of block, and store it on disk. But, it only forwards it if it is smaller than a local max block size setting. Big blocks are thus propagated throughout the network only by nodes that support that size blocks - but all nodes do accept them.
A chain with bigger blocks than the local max block size setting is ignored initially. Transactions in this chain do not show up in the wallet. However, if the network builds on top of that block again then obviously the ignored chain grows. There is another local setting - after how many blocks will you consider the ignored chain the valid chain, even if you dislike the size of it.
It seems as if it is only a small step from here to examine all blocks to see if your transaction is in them. In case of a fork, it could show that it is confirmed in one of the chains but not yet in the other. You can use this for risk management purposes without having to run multiple versions of bitcoin.
Really quite exciting.
This could be the future way of scaling bitcoin (both increasing size as well as decreasing size). But for now, 2 MB blocks will be the most likely next step.