If you can wait a year, you should. If you have to buy something now, you might want to consider getting something really inexpensive, saving most of your money for next Christmas.
Current rumors are that 4K Blu-ray discs might start being available for Christmas, 2015, i.e. a year from now, so that's when compatible consumer entertainment equipment would need to be available: players, receivers and displays. The HDMI v2 chipsets with HDCP V2.2 are not expected to be available to receiver manufacturers until next spring, so AVRs using them probably wouldn't be available until next fall. Many AVR manufacturers tend to release their new models in early summer, though, so I fear many of the 2015 models actually will not be able to ship with full-function chipsets
I really don't think the new HDMI chipsets will be available in time for the Marantz AV8802 pre/pro, which seems likely to be available in March.
(Personally, I'm not planning to upgrade to 4K for at least a couple of years. My 1080p 2D projector is still going strong. I'd been thinking about upgrading the sound system from 5.1 to 11.1 for a couple of years, though, so this summer's availability of Atmos-capabale receivers at not-too-outrageous a price was enough to push me over the edge.)