My post pertains to considerations prior to editing. There are certainly methodologies on how to perform upscaling post-edit, but that's not what I'm addressing here. My point being that handling any artifacts from the upscaling is likely more convenient at the start of the editing process than it is at the end.
That said, when you are upscaling on an export it shouldn't matter if you are exporting to a jpeg or a tiff, assuming that no other manipulation will be done post-export. If you are going to have to apply corrections then I would export as a TIFF, open and edit that at size, and then save off as a final JPEG to save space.