EVFs are improving, to the point where they offer a view that is as clear and bright as the OVF on an entry-level DSLR, albeit with some lag when following moving targets, and slight to complete blackout when shooting in continuous modes (depending on frame rate). They have the advantage of being able to overlay info on the scene and also directly show the effect of changes in exposure settings, although their colour accuracy is apparently not as good as an OVF.

I will stick my neck out here and predict that once Nikon and Canon enter the 'mirrorless' market, this type of camera will supplant the entry level DSLR, with mid level to professional DSLRs still using the current optical system. JMO!