Scarlet isn't most likely going to get any more framerate options with the faster media. Although I would like to be wrong.
As to HDRx for sphericals. Yes you can do it. Yes it's nice for location shots so that you can forget about exposure while shooting reference clips. For sphericals? Not really. You need to be on a tripod anyway so either way you can shoot either HDRx or just use a proMote like we did before. ProMote + NodalNinja + 8mm fishEye is still a really effective spherical capture approach.