I would personally be very content with the implementation of a hybrid EVF in the way that Fuji has done it on the x100s and xpro1.
There are plenty of advantages that I love about having a good EVF (most of which have already been talked about previously). However, the biggest downside (IMO) is having to have it run all the time which is a battery killer. Merely having the option to switch back and forth would be huge.
The other thing that bothers me (which isn't a deal breaker) is the fact that one of it's big advantages can also be one of it's disadvantages in different shooting situations. What I'm referring to is the live preview of your image based on your settings. In most scenarios, this is great. But when you are shooting flash, the advantage becomes nil and actually is a nuisance since the VF goes dark in many scenarios as it cannot account for the light you will be adding.
Before any says it, yes, I know the preview can be turned off. But having to go through menus to turn it on and off in a dynamic shooting scenario can be a real pain.
So for me, there are pros and cons to each type of VF. A hybrid VF is the solution to that as it provides the end user with a choice. On my Fuji, it can be done with the flick of a hardware switch.