There's difference between invalid and non-standard.
Do you really believe that the miners will care about standardness when it comes to $50 million?
Yes, rational pool would consider cost to modify their software to include non-standard TX along with risk about accidently creating invalid block or including invalid TX. They also need to predict whether Ordinals remain popular in future.
Additional Ordinal software can be developed that sends transaction directly to mining pools, and by the way, that's worse because now we have less accurate estimation of the current transaction fees.
That's good point, i didn't think about it. But if pool include too many transaction (which isn't exist on most node's mempool), they can't utilize Compact Block for faster block propagation. It's another trade-off rational pool should consider.