I've seen some comments about the blockchain size getting too big.  I've always wondered why a big chunk of the early blocks can't just be truncated and archived.  I'm not really sure if this is a long term problem.

Regarding the miners processing transactions in the future when the number of BTC awards draw down to zero.  Does the difficulty of the block creation change automatically to maintain a certain block cadence like today?  Or will the transactions be allowed to speed up to facilitate micropayments with merchants in real time?

We're all accustomed to very minimal transaction fees when converted to fiat values.  In the future, will there be sufficient payback to cover the mining costs?  I'm really curious about how this will work.