This is not an op-up upgrade, but rare enough to post it I guess.
I booked earlier this week a return ticket CDG-DXB, Eco Flex, departure in less than 3 weeks
I went on Emirates website to see my booking, and I was offered to upgrade to J with miles for the CDG-DXB leg. 39 000 miles + 40 €

Usually, this kind of offers is very rare, and happens a couple of days before the journey, not like 3 weeks before.

I took this offer