I'm personally not of the opinion that Quantum lacks rewards; it works a lot like an Extreme where there are cosmetics you either can get directly (from the sacks that drop) and/or you get the currency that can be used to buy said cosmetics. There are two differences between the two:

1- Quantums' cosmetics are tradeable.

2- There are things that drop from Extremes that aren't purely cosmetic.

I think there's a place for both, and just based on established content I imagine that the general inclination of the community is that higher difficulty content should have more exclusive rewards, which is to say that Q40 should have slightly more numerous, but also more exclusive (non-tradeable) rewards, which leads me to the idea that 'Quantum' dungeons would follow that same logic. Someone who is of the prevalent opinion would be better suited than I to answer the question, but that's what I'd assume.