Interesting interpretation. Maybe "photorp exhaust" would have been clearer. But if this is where the exhaust of the launcher tubes converges, wouldn't this seriously inhibit the practical use of the airlocks (also from a non-retcon, strictly TMP point of view)?
You mean something like waste heat radiators / dissipators? That crossed my mind, too.
But since you highlighted the same structures on nacelles and neck I am beginning to wonder if it could have something to do with the enigmatic "transwarp drive".
We had never heard of transwarp before, nor had we seen a starship with a fat and strange looking neck like that (okay, we had actually not seen that many starships before...).