If we had the money for both (Kipling to Airport vs. Keele-Dufferin and/or Jane), which would make more sense as a separate line, and which as an extension of the OL?

Hi! Question that I'm sure has been answered before, but if it was too expensive to put underground, why wasn't the eastern portion of the Crosstown elevated? Wouldn't that have made a lot of sense in order to have grade separation across the whole line? Was this ever considered/explored by...