In regards to your request, i dont think that it would be that useful for most users since i assume that the import action is not performed very often. The native way to group the imported tabs should in that case (while a little longer) be "good enough"
1. activating the first imported tab, 2. holding SHIFT 3. clicking on the last imported tab 4. right click on any of the selected tabs 5. in the context menu invoke "Add Tabs to New Group"
If you do perform the import action often and the native way does become to tedious, please get in contact via the the support site and we can discuss if there is something that can reasonably be done
