I think the simple solution here is that if something is in the clipboard, there is an option in the Edit menu to Paste Inside Group if you select a group. It doesn't matter whether it's a regular group or the new maskhelper type group... This allows easily adding objects to the group after it has already been created (not that entering a group and pasting is hard, but people want fewer steps to complete operations).
Martin,
I think the simple solution here is that if something is in the clipboard, there is an option in the Edit menu to Paste Inside Group if you select a group. It doesn't matter whether it's a regular group or the new maskhelper type group... This allows easily adding objects to the group after it has already been created (not that entering a group and pasting is hard, but people want fewer steps to complete operations).