I have not read all the way through this thread so forgive me if I repeat something, but I think the "If I were..." construction is alive and well across the pond. I cannot say "If I was...." and to me it sounds flat and awful.... (Unless of course it's a character and consistent with that's character's other speec da da da da, but I am addressing general usage, and for me it
is everyday register.
Just getting my two cents in.... (Cents of course being currency elsewhere!
And I agree re who / whom -- it sounds forced in any conversation, and the speaker is almost certainly monitoring for correct usage.
Ani