Strongly opposed to a hardcoded constant. Hard forks are irregular. If this proposal had been implemented in Istanbul, the constant would have been 10m, and the gas price would be much higher than it is currently. This constant, like the difficulty bomb, would need to be micro-managed every hard fork, and, in my observation, core developers are very bad at estimating possible throughput.
But I can support removing it from miner control since they have a propensity toward keeping it far below capacity to manage their operating costs. We could consider instead increasing the gas target when it is often exceeded, as that is evidence that miners could handle a higher limit. A higher uncle rate could signal DoS and push down the gas target.