I don't know man, I think this is too strong, personally.
Mob Rule is ace as is, I'd probably try and draw as little attention to it as possible
I also like Mob Up as a stratagem. It gives us more flexibility in how we run our units.
I honestly think we have enough Morale mitigation in our index with Warbosses, Nobz and Mob Rule.
This introduces unnecessarily complexity (which unit is closest, which unit has combined with which again?) and I feel that the current rules are good enough.
Orks definitely need fixes but not here I don't think.