As I could see the business rules for this enhancement being somewhat complicated, a simpler workaround is just to put a shape around the grouped items and have folks vote on the shape itself.
Yes this could work as a work around. However when facilitating a session of 22 people with a multiple number of improvements it will be time consuming to do this during the session. And I do wonder if this is indeed that complex to realize.
I think the problem of the workaround is either that everything has to have a shape and limit voting to shapes and this would slow a retro or other discussion down.
Ideally something like this would exist:
Pull stickies together (grouping)
Start voting, if there are touching stickies they are in the ‘sticky group’ - automagically group the stickies
A workaround we use to group and then turn one of the stickies into a different colour and ask people to vote on only Dark green coloured stickies … of course some people just don’t listen anyway!