The coming standard claims "up to 2GB/s possible." [1], and at this "speed" (of adoption, that is), this is not coming anytime soon.
[1] https://www.pcworld.com/article/2124706/sd-express-9-1-new-s...
SD card users who care about speed have UHS-II equipment, but SD Express and UHS-II use mutually incompatible high speed signalling on the same pins (so cards and readers are only supporting one of the two - I guess technically this could be fixable with special purpose chips, but at large cost).
Users who care about speed but not about SD card compatibility are already using CFExpress, which is supported by most modern professional cameras and has much better hardware availability than SD Express.
"The upcoming 2TB card, dubbed the 'EXCERIA PLUS G2' is said to have read speeds of up to 100 MB a second and write speeds of up to 90 MB a second. This 2TB size now hits the upper storage capacity of the defined SDXC standard."
Not sure about IOPS but if you're streaming media or large game assets, sure that's fine.