I don't see any conceptual reason why an Anand Kaaraj cannot be held outside, as long as full Satkaar, cleanliness and Maryada for Maharaajh are guaranteed to be followed at all times. Maharaajh's saroops are taken outside in outdoor programmes across the world, as well as camps and to peoples' residences.
The objection is against taking Maharaajh to where it is known that Satkaar and Maryada will not be followed, e.g., party halls where booze and dirty songs are going to follow - that's where the prohibition on no Anand Kaaraj's outside Gurdwaras should apply.
If the utmost Satkaar and Maryada for Maharaajh is followed at all times, then I see no reason why the Anand Kaaraj cannot be held outdoors ... or am I missing something?
Bhul Chuk Maaf,
Waheguroo