Question of dielectric coatings on primaries.

I am well aware of thr concerns about enhanced aluminum coatings - everyone from Royce to Swayze to Zambuto rails against them. However, what about Dielectric coatings on primaries? The finest diagonals utilize these as do critical low scatter laser and multiple reflection apps. Now true once applied these coatings must often be polished off. Therefore, a bothched coating job can result in a ruined mirror. But if these could be reliably applied what would be the down side. Obviously the upside is 99%+ reflectance. Thoughts?
Joe

I talked with a man that does Dielectric. One of the problems is the size of the primary vs. the size of the chamber. The other is the cost factor which is very high. Finally there is the deposition of the material onto the mirror vs. size of the surface that makes it hard to get a mirror over about 6" to coat evenly.
This is what I was told anyway.