The other is that the basis of this rumor seems to be based on the fact that there is 5K resolution options in OSX Yosemite. What if those resolution options are for a external monitor connected to a compatible Mac via DP or TB and have nothing to do with the iMac. Also it could be the resolution of a new Apple Cinema Display. That would make more sense IMO.
That's a good point. Apple probably doesn't want to get stuck in the position that they were in early on with 4K support which was a bit sketchy initially. In fact it still is a bit sketchy with some existing models or rather most existing models with respect to their hardware. Software is an easier fix so why not account for 5K support now in an upcoming software release (theoretically speaking).
It makes sense that the upcoming Dell Ultrasharp 27" 5K 5120x2880 monitor would be supported in developing software given that its already mature enough to be demoed and is probably fairly close to final hardware itself. Apple supported with specificity a subset of 4K monitors initially:
- Sharp PN-K321
- ASUS PQ321Q
- Dell UP2414Q
- Dell UP3214Q
http://support.apple.com/kb/HT6008?viewlocale=en_US&locale=en_US
The Sharp and the Asus are essentially the exact same model.
Still the Dell 5K will supposedly require dual DisplayPort 1.2 inputs which means any Mac that would support it would need to use dual Thunderbolt ports. This assumes any such Mac has the GPU prowess to power it.
So yeah, I agree, this could just be Apple trying to support the upcoming Dell 5K monitor or their own Apple 5K display. I expect a ~$2500+ to ~$3000+ price for any stand alone 5K monitor at ~27".
It should be no problem for the new LGA2011 based Mac Pro to push such a 5K monitor as well as an updated Mac Pro based on Haswell-E / EP LGA2011-3. However, the rest of the lineup is probably going to need to be totally updated.
That's not to say I don't think we could see a 5K iMac but that would be a tough bit of engineering (maybe using a combo of Intel iGPU and mobile nVidia or mobile AMD GPU or new yet unreleased GPU).