Looking on eBay I see there are component to HDMI adaptors. Maybe with this and a HDMI to Displayport adaptor you will get the solution you need. I have never tried this, so I can't say if it will work.
For me the problem is simple: closed ecosystem. For this to work it needs to be like the iOS: extensible with third party apps and channels. Until I can choose between options such as iTunes store, Netflix, Blockbuster and pure web based streams, then solutions like XBMC and Plex will still be more appealing, despite the need for better hardware.
Whatever the real problem is, clearly this another point that Awhen pple is going to become meticulous about. Most times, when sufficient people have complained about some issue, Apple appears to have made an effort to address it in the next generation, especially those getting media attention.
I will be curious to see the impact of the next point point release.