Actually! (Full disclosure: I sell access to a Tahoe-LAFS grid.) The Tahoe team has recently been working to merge the "cloud-backend" branch, which would open the door to storing shares on grids by interfacing directly with S3, GSE, etc. This technology's been battle-tested by Least Authority Enterprises, and at least Matador Cloud has indicated a desire to adopt it as well. Other Tahoe vendors are probably sitting up and taking notice too.