If 3D is important to you, Look at the E6 OLED as that has one of the best 3D performance of any 4k HDR TV.
HDR itself is far more than just a 'brighter' image and far more of a step up than 4k is from 1080p and I would argue more than HD was to SD. 'Good' HDR, not the HDR offered by 'budget' 4k TV's which at most only offer a bit more 'brightness', is impressive and that's with screens offering at least the minimum standards for HDR10.
Peak Brightness is just 1 aspect but its part of the aspect governing Contrast Ratio. At the other end is black level which is equally as important. Not only does HDR offer more lifelike contrast ratio with fantastic specular highlights but it also adds details in the dark areas. Instead of black blobs in the shadows, you now get more definition of the objects in those shadows. HDR also has a wider colour gamut too. Colour is more than just the value(s) of RGB but also has luminescence (brightness). A white piece of paper for example and white hot steel may have exactly the same RGB value but White hot steel has far more luminescence. Sparks (like electrical or grinding metal) and lightning, Fires etc look absolutely in HDR and much more realistic too. These 'glow' with the richness of colour and luminescence of real life. HDR TV's have a much greater colour volume.
At the moment HDR is in its infancy and like 3D was, there are some very good HDR content but also some that are mediocre at best. When it works well, the images are absolutely stunning and vibrant - most of 'demos' for example for HDR TV's are incredible (LG's Chess and Jazz are amazing) but there are a few examples of HDR that can be underwhelming. As a gamer, the HDR games I have played look stunning - Gears of War 4, Ratchet and Clank, Uncharted 4 and really looking forward to Horizon and Mass Effect next month.
HDR is certainly here to stay. I think every 4k TV releasing in 2017 will have (or at least support) HDR. The UHD alliance, HDMI and even broadcasters (with HLG) are all planning for the future and bringing HDR to the forefront. Its not limited to 4k either as its standard also include higher resolution.
Whilst 3D may 'appear' to be on its last legs - at least as far as domestic Televisions go and maybe even future releases of Blurays, I know that a number of people still want and/or have a collection of 3D content. If I was in that position myself, I wouldn't be looking at just a 4k 3D TV but looking at the few HDR10 TVs that offer 3D as well. Money no object, I would almost certainly opt for the E6 OLED but if tat was beyond my budget, maybe the Panasonic DX902 or Sony 9305. If you don't mind curved screens, then the C6 OLED might be a good alternative too. Regardless, I would still be looking at a HDR TV as I think that's more future proof and the likelihood that's where TV's are likely to go. I don't think HDR will be an 'extra' as such but become the 'standard' of content at those resolutions - much like SDR was the standard for SD and HD content.