I'm weighing the same decision. It's time to replace my eight year old Mac Pro, and I'd like to go with a laptop + docking station + external monitors, but I'm torn as to weather and get the current model or the next.

I've decided to wait. The current model will be discounted, and I want to know how many USB-C ports will be on the next version and what the impact will be. I've heard it is painful if not impossible to connect older Cinnema dispays to mac book via USB-C.

Edited to add:

>-I want to do iOS development You can do iOS development on any intel-based mac. My 8 year old mac pro is fine. My Macbook Air is perfectly fine.

>-Want to be able to hook up a external monitor later, >hence the MBP and not air

You can hook up an external monitor to any of the modern macbooks, you just have to purchase an adapter. A mini-display cable will plug into a thunderbolt port, and there are adapters for other cable types (thunderbold to vga, thunderbolt to DVI, etc). I have a set of adapters I carry in a bag just for presentations.

If you want to drive 4k monitors, there be dragons.