Macbook Pro (r)'s aren't equipped with 4K screens, so it really wouldn't make a difference at all for people who buy them.
As far as the zoom feature, again, downscaling is a process that is applied spectrum wide to source material, so when it is downscaled, the zoom quality is not retained...it is also downscaled (and thus, quality diminished). If you're talking about zoom function while recording the video...this is another downside of the functionality on a smart phone...the zoom function will not operate like you find on true depth 4K cameras on the market...you'll be limited to the device's sensor size (just like on the cameras found on all smart phones, even the high end Lumia camera hardware).
Let me be clear...I won't be unhappy if they decide to include 4K recording abilities (as generally useless as it will be), I will be a bit disappointed if the still camera isn't polished up as a better function though...and that tends to be the move when these kinds of features are put in. Makes it easier to sell a product when people are wow'ed about the newest tech...when the reality is making the still camera even more optimized would be a far more useful addition, and people would enjoy it more (even if they didn't get wow'ed as much by it vs. a gimmick like 4K).