I would guess that it won't. The 975 has been out for about 5 years and 4K hasn't been available that long. There is an interesting statement though in the original release announcement about a "bypass" mode which passes through video unaltered.

"More importantly, the Model 975 includes video scaling so that 480i analog sources will be converted up to 1080p for use with the vast majority of video displays that cannot accept 480i via HDMI. Flipped around the other way, for games or sources where you want to take the processing out of the signal path, the Model 975 also has a "bypass" mode that sends the video straight through without any alteration. This provides you the best of both video worlds in a way that even some higher priced products no longer accommodate."