I have a 5040UB along with an Elite Screens Cinegrey3D 120" screen and thought I'd pass along my own findings as it seems to have uncovered a few details that have not been reported here. If i missed it and I'm being redundant, sorry about that. By the way I also have a 5030UB which after at least a couple years of use now is about ready for a bulb change (already have the bulb), but the idea of HDR and expanded color gamut regardless of resolution caught my attention and i had some unexpected extra cash to put into this hobby so i jumped the gun. After receiving the 5040UB and setting it up to compare with the 5030UB my initial impression was Wow! Much brighter ECO setting, and closer to spot on color and noticeably better contrast right out of the box. It also took a lot less panel alignment adjustments on initial setup than my 5030 did.
The first problem i encountered was in trying to get any sort of HDR signal from the Samsung K8500 Bluray player to lock with the PJ, but not only that, the BR player would enter 3D mode any time i tried to switch the resolution from 4K to 1080 or any other setting and had to be factory reset to fix it. 3D? I didn't even have a 3D disc in it at the time. Needless to say stay AWAY. I got on the phone with Epson support and they said to get the Philips UHD player and call them back about the many features that didn't appear available (greyed out) on the PJ. The Philips UHD player was able to handshake with the 5040 in HDR mode, but only under these circumstances:
HDMI 1 only, HDMI 2 on the Epson would always handshake at SDR regardless of settings.
4K 60P had to be completely shut off in the settings of the Philips player
Resolution could not be set to 4K, but rather to Auto on the Philips player
All Advanced image settings had to be set to "Auto" on the 5040.
Picture in Picture is lost any time a 4K signal or 3D signal is present on either port according to Epson...however i was able to get PiP in a very color-distorted window with one 4K source.
So even if you have a 4K/60p capable BR player and disc with HDR UHD, you can only view it in 24P, and not 24P refreshed at 60Hz so that Frame Interpolation could be used to brighten it a little and smooth the motion. The Epson tech support rep admitted even they were trying to figure out all the missing details in the documentation of this PJ's capabilities.
While i haven't tried the very very limited HDR capabilities in a complete black room yet, i can say the image looked extremely dim and like a thin film of milk was spilled over it. Not what you would expect from a technology created to expand the Pop from the range of color and B/W contrast, just the opposite. I usually like to start with an image that is reasonably close to good enough and calibrate from there - but i see no use in even trying to calibrate that awful looking picture.
All that said, the SDR 1080p or upscaled faux K looks about as good as anything i've seen to my eye. Having the right screen, viewing distances/angles/throw are important in this, and on my system i'm very impressed with Non-HDR performance...trouble is, i already had a projector that could do that well even if not as well as this one. I think the 5040 will be going back and i'll be waiting and letting my $3k grow to about $3005 in a savings account for the next year.