Q: Why doesn't the iMac (Retina 5K, 27-inch, Late 2014) support Target Display Mode? And what are my alternatives for using it as an alternative for my mid-2012 MacBook Pro? (both running 10.10.3)

Have you seen this:

Thunderbolt Firmware Update 1.2: Keeps reappearing and Thunderbolt ports and Target Display Mode may not work - Apple Su…

TDM is not supported on that model, for whatever reason, and it's never going to work. If you bought it directly from Apple and you're within 14 days of delivery, you can return it for a refund. Otherwise, you'll need to buy a display. Screen sharing won't be a satisfactory substitute because it's too slow.

Just read this post and I'm really shocked. I have a latest MacBook Pro and just got myself the 5K iMac. And I was pretty sure I am able to use target display mode.

Is there any chance that Apple is going to work on this topic? E.g. using 2 Thunderbolt cables? I mean this was one of the benefits using a Mac and a MacBook together. I can't be bothered to spend 1000USD+ for a Thunderbolt Display and having to big displays crowding my desk!!!!

Apple will be making the move to USB-C and Thunderbolt 3. Of course then you will need to buy two new machines that support those if they decide to bring back TDM.

ArSu77 wrote:

 

....I can't be bothered to spend 1000USD+ for a Thunderbolt Display ....

There are a vast number of displays that are far cheaper than the TB display.

Also, you could connect the "extra" display to the new iMac and be able to work

with 2 screens when not used with the Macbook.  I think you will find that once

you start working with two displays, you will wonder why you didn't do it sooner.