Also fair to consider that the "die hard" fans have already gone through much of the previews which will help keep lines pretty reasonable. I'd venture to guess that a huge portion of the guests at the park today already went during the previews and are mostly there for the bragging rights of being there opening day (along with the exclusive opening day events/entertainment and merch).
Universal must be satisfied with the attendance currently, otherwise they would have opened the option for pass holders to add on EU to their AP and/or started offering multi-day passes with park hopping privileges which include EU. Until that happens, every single person you see in the park paid $140-$200 just to go through the gate for that one day. I (personally) would hold out on making any judgements based on queue times alone until both APs can add on EU and EU is included with all multi-day tickets w/ park hopping.
FWIW, as of this posting, there is a digital queue (short, but still) to buy EU tickets which seems a very positive sign.