I was also looking at the smallHD DP4 as I already have and love the DP6. But you need a powered HD-SDI to HDMI convertor like the Atomos Connect or one of the Blackmagic products like the Battery converter:
http://www.blackmagicdesign.com/product ... onverters/For me this just added additional elements that I did not want (and added cost). So I went for the Alphatron EVF made by TVLogic. It have both HD-SDI and HDMI input and output.
It's great. The battery cover sucks tho. Only thing I miss from the smallHD DP6 is the Focus Assit Plus.
smallHD said they had an HD-SDI version of the DP4 in the works but it's never materialised. I think they have been working on the DP7 tho...