Years back when the /follow issue first came up I left a suggestion with them that would work for us.

1. Reenable /follow everywhere for toons on the same battle.net account.
2. Add scaling penalties for each concurrent character on the same battle.net account. Like damage nerfs as more toons get added.

This way you could choose the penalty as-is which is loss of follow on your deathball or have all /follow functionality back in all content with scaling penalties the more you have. Such that with 8 concurrent sessions you might be doing 2/3rds the damage you currently do.

Ideally you should be able to dual box and have no penalties anywhere. It's just short sighted to punish a dual boxer the same as a 40 boxer.