The fact is the 13" is a dual core and has integrated graphics, which ever way you look at it its hardly a pro machine and isnt overly powerful so doesnt really seem like a decent compromise anymore. All the 5K imacs are quads with dedicated graphics and you get the 5k display. Pretty much all of the imacs will run circles round the macbook but obviously you cant take it with you.
TBH as a desktop competitor/replacement the 15" is a better option, for only a couple more hundred £ you get dedicated graphics, i7s as standard and a bigger display. Much better value for money when the 13" fully speced is well into the £2ks. The gem in the line up is the 15" 2.9 with 512gb SSD and RX 560 with 16gbs of ram. The are retailing for £2699 or £2289 in the refurb or £2389 on amazon. You get the portability within reason with most of the power.
The issue with the 2017 models is the keyboards are super fragile and how useful is the touch bar?
The ipad Pro still doesnt offer any of the pro programs you mention and is a glorified media consumption device that costs as much as a laptop. For the time being its no match for either the Macbook or the imac simply because it runs IOS. Although the pen functionality is amazing just a shame it runs IOS and it cant be integrated to the mac ecosystem in pretty much any way, like using it as a tablet for example the full version of lightroom by attaching it to a computer like a wacom etc Obviously there are IOS alternatives but non of them give the full power of a desktop app so as a pro its difficult to advice anyone to buy one over a laptop.
Although the macbook isnt as powerful its is a bit of a dark horse, the i7 is within 10% of the 3.1 macbook pro and is a much neater package. Obviously comes with its own drawbacks like the single port and relative cost of entry vs the macbook pro. Looking at the 13" macbook pro it doesnt really add much over it, not much more powerful, integrated graphics less portable but has more ports which is the god send.
TBH most pros will use both. As a compromise I have always had a lightweight laptop and a workstation. I used to have an 11" MBA maxed out and a Mac Pro. The MBA was stolen unfortunately so I switched over to the base macbook. I realized I dont really do any serious work on the road, more moving data, organisation and reviewing images (im a photographer), I can do that on the road and edit the odd image and then do the hard work once I get back to the desktop. The main downside is the single port and needing to have power to plug more than one device at a time which for me is a big headache. Otherwise its a good machine with the retina display, the size of an ipad, it can stand on its own so is great for media consumption, really great speakers and there is almost 0 penalty to taking it with you. The main benefit is it runs OSX so runs all of the desktop apps which is pretty much the deal breaker for me.
The new machines should be released in June, the 13" is meant to be getting a quad core with integrated graphics and the 15" a hex core. All the iMacs will be hex cores too so for the same money you will get significantly more power.
Im waiting out on the Hex imac to decide whether I buy an iMac pro or the iMac.
If you can hold out it might be worthwhile for the 8 or so weeks.