I agree incentivizing backup witnesses is a good move. I love how markets and price signals work that way. :)
Without incentive, backups will turn off and if there's a massive flood of new users or a drastic change in price, structure, or something else which needs immediate change, there may not be new witnesses willing to go with the change ready and willing to be voted in.
That said, it's early days so I'm willing to be patient and see how things work out.