May be you guys will have better luck with it. I will try the sleep to see how that works now with this. I did not see any issues with the Yosemite version of the kext. But it is too soon for me to say though.
I got the display port working by patching the AppleIntelFrameBufferCapri.kext manually. Now it detects the external monitor properly and supports full resolution via that port. Also detects audio port (verified via DPCIManager, but did not test actual sound output).
The HD4000 card in surface has the revision id of 0x0009. So i modified the kext above for that platform id to support the LVDS in surface pro and modified the DSDT and the config file to inject 0x01660009 instead of 0x01660004.
Let me know if there is any interest and i can post the the files used.