There are much easier and cheaper ways of generating megavolts of electricity, I think the biggest barrier would be getting someone who knows enough about this to build it despite their skepticism about the validity of it.
They found a use for it in particle accelerators to partition off sections that are under vacuum
That was my first thought - the military would be all over this if there's even a remote chance you could build energy shields or something.
Electrostatic precipitators exist but they aren't large. Everything else I'm aware of that works on larger scales fails to satisfy the uniform/gradual aspect.