If I remember correctly there was a lot of discussion about that, back when the project started last year. And I think out of simplicity we decided shells should not be connected physically. The shells are separated by walls and because they are not part of the shells you can't edit them or remove them.. However you
could connect shells underground... This has never been stated as an explicit rule, but technically I see nothing that would prevent it; you would just need to make sure it is at least 10 feet bellow those street walls. (Also you could only do it under those walls and not under the streets or the courtyards..) If you like that idea we could make this as a firm rule.
I guess if there were many requests to be able to physically connect shells on floor level I could do something about it.. That would require me to change the street walls and include them in the shells. And that would also require people who already have their shells and who want to connect them to update their own files (although that wouldn't be difficult). However I couldn't do it on all the walls because some of them are decorated (like the waterfalls) and I really don't want to see them destroyed..
Maybe we could have a rule where you can connect shells above the walls? With bridges or similar things.. It would need to be only inside a specific area, but I guess that could be possible.. What do you think?
Connecting shells through interractivity shouldn't be a problem however. You can push a butto in shell A to open a door in shell B. There's no problem with that. You would just need to find a story to explain how it works because the shell's aren't physically connected.

(Wi-fi technology?)