When will come the new raw version update for Adobe Lightroom 4 with Nikon D750 support?
There won't be an update for Lightroom 4. The only way you can work with your D750 raw files is to use the free standalone DNG converter to create DNG copies. If you want to be able to work on the NEF files then you will have to upgrade to Lightroom 5. Lightroom does not use the Camera Raw plug-in. Everything is part of the Lightroom program. If you want to stay current with Lightroom then you need to follow the update/upgrade path. That means purchasing each new major version of Lightroom or subscribing to the creative cloud plan.
Although really, really annoying. :-(