Punch holes in this idea. Just a thought.
If the hash rate stabilized, I believe we'd see much higher tx fees. I'm fine with that personally.
It already works that way doesn't it? when the hashrate decreases, the difficulty also decreases (less computing power competes for the next block, which is added every 10 minutes), so with the same amount of computing power you will mine more bitcoins in the same time, which increases the profits of miners, which attracts more miners, who fill the gaps left by those who left.
tx fees do not depend on the number of miners and their hashrate. New block is added in every 10 minutes and adds transactions with the highest tip for miners. There is no hashrate in this equation.