Thanks everyone for posting this to our ideas forum!
I've done some research internally on UPS Worldwide Economy and it is a service class we would very much like to add. In fact, some foundational work has already been done so we can implement it in the future. But this service is not included in our current UPS partner contract and because WW Economy is a container class (rather than individual parcels), there is some platform work that needs to happen before we can add it in ShipStation. There are other container class initiatives we're looking at as well, so this platform work will be beneficial for several integrations, not just UPS.
There is no ETA for implementing this right now since other projects are currently on the immediate roadmap. We'll update this thread in the future when we have more details. In the meantime, we'd still like to hear from other ShipStation users that would like to see UPS WW Economy services in ShipStation.
This is hanging there since 2020 and still no development? Unfortunate.