4K is useless for anyone but videography and aerial photography professionals. 1080p is good for the majority.
here is the reason why:
1. Most people have phones where 4K doesnt look as good as a big screen and 1080p looks smooth and crisp. Most phones today cant even handle 4K resolution
2. Most Monitors being used dont use 4K and 1080p look the best due to 4k looking jagged due to smaller pixels on non-4K monitors
3. Most Phones and machines today cannot play 4K content
4. Most Machines today cannot even handle 4K editing let alone 4K downsampling which takes huge system resources.
if you get 4K without really needing 4K you will likely spend 500-1000$ to have a machine and monitor which can play and edit 4K video.
I can see 4K becoming standard by Phantom 4 where its camera will have 4K on the base model and the higher end model will have other features.
2015 there is no use for 4K when I know the machine to edit it and the media devices to play it are very expensive and in its infancy. I would wait till 2016-2017 when 4K monitors and capable machines and televisions are in more homes.
Right now 4K is only catering to about 10% of the mass audience and thus not worth the money. it will be in a year or 2 but not right now. I would save and get a Phantom Advanced and 2 additional batteries or 1 battery and a backpack than to purchase a Phantom Professional.
Wait a year when 4K adoption is more, the Professional is not future proof because the new quads will come to the market every year and P3 will be obsolete by P5 completely.
TLDR, no need to purchase 4K to cater to the niche product as of today.
why not save money now and buy 4K when it does become more common in 1-2 years. Right now a year before P4 unless you are a professional videographer, its a waste of money to be honest.