Hello again. @kayb: sorry, I missed your post earlier. I'm using 80% less coconut oil by weight than butter. I don't think this is an issue of too much coconut oil. Do consider there are plenty of recipes using melted butter, so whether coconut oil is melted or not is less of a concern - here, it's likely technique, and going through all this I'm certain I simply overmixed . FWIW, with these cookies, the coconut oil was soft, but not fully solid or melted. There was a different recipe I tried with a more solid coconut oil and chilled bowl during creaming, it didn't work as there were chunks of coconut oil in the resulting dough. I think this is because coconut oil is not like butter in that it doesn't have a plastic-like phase.
@teonzo: on a total tangent, it's past 2am now, I woke up thinking about your comments of the mayo and sugar, and had to post: I don't think that air is introduced into mayo.. a mayo is as you say an emulsion, where we force a suspension of oil in water or water in oil situation. Maybe a little might be since there's fast mechanical action, however, it's not like creaming butter with sugar, or making whipped cream or egg white meringue, where air is part of the mixture; there's also a substantion increase in these, whereas I don't think I've ever noticed a volume change making aioli. That said, I do agree with you that over mixing the mayo and sugar would lead to breakdown of the emulsion - this makes sense, especially considering sugar is hygroscopic and would probably suck the water component out of the mayo separating the oil.
BTW, I did try some basic google research, and wasn't able to confirm or deny whether mayo is aerated. What I wrote is just conjecture at this point, so I am curious to hear whether I'm on the right track.
This is fun, thanks for the discussion 
