For bitcoin to be peer to peer cash, as we all know, it will need to scale with regards to transaction capacity per second.  Obviously this can be addressed through off chain solutions, but I am curious about on chain scaling.  

As I understand it, there are only a few things that could be done to increase on chain capacity without drastically altering the protocol.  

1) You can increase block size.  The major argument against this seems to be the burden placed on running a node, which would increase centralization by making it harder/more expensive to run a full node.

2) Segwit, which makes more efficient use of a given blocksize, and is already implemented.  (I am not well versed in the technical arguments against segwit)

3) Alter the protocol to increase the rate of block production, and decrease the block reward, such that money supply is the same, but you end up with more transactions per second for a given block size.  This would appear to have all the drawbacks of 1), and also an increase in the orphan rate. [/li]

Are there other ON chain solutions being considered?