If a product needs to be added/amended/deleted in 2 CMSs (for 2 separate websites), the whole process has to be done twice, once for each CMS/site. A way to (i) copy between CMSs or (ii) export from one CMS then reimport into another CMS would be a big timesaver
Technically this would be extremely difficult and only a handful of customers have separate databases with the same products in for multiple sites.
In the medium term there will be improvement in the new importer (about to be released) which will allow product(s) to be exported and the re-imported. This mechanism could be used to copy products.