Sony's intent is to dominate this market and this is a segment that has been identified as a strategic growth area, based on how they are pushing these products (with constant presence on the road of folks like Toru Katsumoto and Masashi Imamura - who are the top bigwigs in their Imaging arena). I don't think they will compromise on things like the EVF etc and introduce products of an overtly lower spec than say something from Panasonic.* I have looked at the Olympus and Pana clip ons and the Samsung NX10 EVF. The one in G1 is a cut above all these.
I would look at the EVF that is present in the NEX camcorder, to have an idea of what the specs on the clip-on EVF would be like. The 16mm's OVF is something I personally would not even bother to purchase, to be quite honest, even though it does look like a well built product - I don't consider it useful enough.