Below you will find general information and a link to a table directly from Rackspace outlining feature comparisons between Rackspace Open Cloud and Rackspace Legacy/First Generation.
With regards to Rightscale, the Rackspace Open Cloud will have full feature parity carried over from the Rackspace Legacy cloud. The only major addition (at first) will be the inclusion of block devices/volumes, which are unavailable from within Rightscale when using the legacy cloud.
Aside from that, a good table of comparison data between the two cloud platforms can be found directly on Rackspace's support site.
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