As the author of a popular SPV wallet, I wanted to weigh in, in support of
the Gavin's 20Mb block proposal.

The best argument I've heard against raising the limit is that we need fee
pressure.  I agree that fee pressure is the right way to economize on
scarce resources. Placing hard limits on block size however is an
incredibly disruptive way to go about this, and will severely negatively
impact users' experience.

When users pay too low a fee, they should:

1) See immediate failure as they do now with fees that fail to propagate.

2) If the fee lower than it should be but not terminal, they should see
degraded performance, long delays in confirmation, but eventual success.
This will encourage them to pay higher fees in future.

The worst of all worlds would be to have transactions propagate, hang in
limbo for days, and then fail. This is the most important scenario to
avoid. Increasing the 1Mb block size limit I think is the simplest way to
avoid this least desirable scenario for the immediate future.

We can play around with improved transaction selection for blocks and
encourage miners to adopt it to discourage low fees and create fee
pressure. These could involve hybrid priority/fee selection so low fee
transactions see degraded performance instead of failure. This would be the
conservative low risk approach.

Aaron Voisine
co-founder and CEO
breadwallet.com