For me that would be pointless, I use the Storage card to move games between multiple machines, I'm sure MS said they would allow other manufacturers and sizes so eventually there will be more options. However for now it's a pretty convenient solution for me as you get more space than the internal drive.
It's still a lot more expensive than if they went with standard external SSDs. Having it be exclusive to a few brands really jacks up the price. I doubt it's going to ever be as cheap as an NVME that you can buy for a PC.