Say that the date for counting votes is 3 months from now. Every one who wants to cast a vote must lock coins until the vote closes (using CLTV). To increase the weight of your vote, lock more coins. Write your choice in the scriptPubKey or an OP_RETURN data output.

On the date the vote closes the nodes tally up the coin values for the various vote options, and the choice with the highest total is the winner.

Not saying this could be used to solve the block size issue necessarily, but we could have choices like:

1) Keep block size the same

2) Reduce block size by 10%.

3) Increase block size by 10%.

The vote could be a rolling one. When the present vote is decided the vote for the next 3 months starts.