The pg_upgrade experience right now is a bit as if you woke up in the
morning and found that city officials came by during the night and
renumbered your house, thus changing your address. Then, they sent
change of address forms to everyone who ever mails you anything, plus
updated your address with your doctor's office and your children's
school. In a way, there's no problem: nothing has really changed for
you in any way that matters. Yet, I think that would feel pretty
uncomfortable if it actually happened to you, and I think the
pg_upgrade experience is uncomfortable in the same way.
It's more like a lot number or surveying tract than an postal address. Useful for a single party, the builder or the government, but not something you give out to other people so they can find you.
Whether or not we copy over oids should be done based upon our internal needs, not end users. Which is why the fee that do get copied exists, because we store them in internal files that we want to copy as part of the upgrade. It also isn't like pg_dump/restore is going to retain them and the less divergence between that and pg_upgrade arguably the better.
David J.