HDR-capable projectors already exist in select commercial cinemas. I believe it's only a matter of time before this trickles down to the consumer level.
Scott posted an article that explains how HDR projection might work. It involves using additional optics to mimic the effect of local dimming. Done properly, this could allow you to get much brighter highlights without sacrificing blacks. However, as with FALD LED/LCD's, the control of the "backlight" is limited in that it doesn't get you down to the individual pixel level. Instead you get a number of "zones".
Yes, there would be more light "wasted" in scenes where small specular highlights appear in a zone which also contains darker content. However, if the majority of the image is dark then there may be less light "wasted" in the other zones where high light output is not needed if the optics do a decent job of focusing the light where it is needed.
While most current projectors don't come anywhere near hitting 800-1000 Nits, some owners may still be able to benefit from the ceiling being raised on light output. Regardless of whether or not your projector can hit the desired light output for highlights, there are still two possible benefits...
1) HDR is supposed to use a minimum bit depth of 10 bits per primary versus the 8 bits per primary used in most SDR content (including Blu-Ray). My understanding is that they have spread those additional 2 bits across the range, improving gradation in the SDR range of light output as well as adding more values to the top end. In fact, I believe the gradations are actually finer at the low end than they are at the high end to better match our visual system's perception of light. The PQ curve is an integral part of this. So long as your projector can accept a native 10-bit signal and the projector/player are able to "speak the same language" then contouring should actually be less of a problem than it is with 8-bit video content.
2) Some projectors may benefit from the wider color gamut used in the grading of the content, even if they can't take advantage of the additional steps in lumenence.