Oh boy. Let me put it this way.
When I hear you say "you should advocate for making the attic conditioned space" all I can think of is - why? Unless you are going to actively use that space for living, that's more air to heat and cool.
And we're stuck with some circular logic. You say it's fine to put air handling stuff up there, but that only makes sense when that space is conditioned. Which I believed you agreed to early.
I'm saying... just don't.