Aloha Stadium is likely the only venue with the capacity size to satisfy the UFC.  However, there are many logistical issues that the open air stadium presents that make it an unlikely event.  For one, the UFC would probably want the fights to air in prime time hours on the mainland.  That would mean the feature fight happening around 5p to 6p Hawaii time.  That means prelim fights starting around 1p Hawaii time.  Fighters aren't going to want to fight in the mid-day sun and heat.  So, at minimum, you need to shade the ring.  The problem with that?  It blocks viewing from basically all upper levels of the stadium, thus severely limiting capacity.  That's not even considering the distinct possibility of rain/wind.  This would be one scenario -- among many -- where a 25,000 to 35,000 seat stadium with a retractable roof would be ideal in place of Aloha Stadium.