Just as the very early generations of the floppy less iMac were inconvenient, and the first Macs with no DVD drive were inconvenient, a "dongles for everything" MacBook Pro is going to be inconvenient. In the end, Apple's generally right about what ports to drop, but the first generation of a severely pruned machine is often a pain. They drop something that people still count on to pass you files, then they turn out to be right a couple of generations later. 2016 was the FIRST year that no student tried to hand me assignments on CD or DVD (I teach landscape photography at a large public university). Students mostly don't have burners any more, they don't expect faculty to have readers, and the university has improved its campus file transfer system to the point that e-mail attachments and campus file transfer combine to 70% of what I get electronically (the remainder is USB sticks). The first year of no DVDs, though, I was getting 50% of my electronic assignments on CD or DVD.
The counterexample is the way they dropped FireWire. They let us know it was coming for years, then they went from multiple ports including FW400 and FW800 to a single FW800 port, then they finally moved it to a Thunderbolt to FireWire dongle on the Retina... I never talked to anyone who minded - the dongle worked pretty well, and Thunderbolt had been around for a couple of years, with Apple sending a clear message to buy Thunderbolt storage. The Retina models lost both FireWire (expected) and Ethernet (unexpected and more painful - I'm not sure that one is fully compensated for FOUR YEARS LATER - there are situations when Ethernet is much faster than (most) wifi - yes, there are fast access points that can beat it, but good luck finding one at universities and other large institutions, which have a lot of Gigabit Ethernet ports).
Losing Thunderbolt 2, which I'd consider highly acceptable, would be kind of like losing FireWire 400 (while 800 still existed), except that the adapter is much more expensive than a 400-800 cable (although it's still cheap compared to the majority of Thunderbolt storage out there - most of it is big RAIDs)... Realistically, a lot of the RAID problem will be taken care of by docks, which can easily have a Thunderbolt 2 port.
Losing conventional USB, on the other hand, is a much bigger deal, since it is something used by a lot of fairly inexpensive devices to transfer data around (and people hand you a USB stick without thinking "does your computer have the port for that")? In terms of data transfer, it's more like the first generation of no-floppy or no-DVD Macs, which were notoriously inconvenient. I'm willing to re-case or re-cable my own storage (and buy double-ended memory sticks) to deal with USB 3.1, but I want convenient access to other people's memory sticks, and I want a SD reader that is as simple as possible, built-in if possible, but one piece for sure - NOT a "stick a dongle on a reader then plug the damn hydra in" situation.
HDMI is somewhere in between these two - it means carrying a dongle any time you have to deal with a projector (if you OWN a projector, you may well be able to find one with USB-C (and you can certainly put a USB-C cable on your own projector to avoid a two-part connection), but it will be YEARS before these become standard in conference rooms, classrooms and meetings). The university I teach at still thinks Mini-DVI to VGA is a "Mac adapter" - even though Apple moved to Mini DisplayPort by 2010 or so, those adapters still aren't common in classrooms or what the library hands out - there are some around, but you need to know who to ask. Most of our projectors are finally HDMI as well as VGA - there are still a few VGA only dinosaurs around...
How long do you think it will be until USB-C to HDMI adapters are in every classroom? Until there are, faculty (and students making in-class presentations) will have to carry TWO USB-C to HDMI dongles, since they break. Not as bad as having to dongle a USB stick or use a two-piece SD reader, but not trivial like using a different cable or a dock on a RAID that probably isn't portable anyway.
In "payment" for dealing with these hassles, I'd want a radically improved machine in other ways. Thinner and lighter aren't my priorities, when the Retina MBP is already a thin and light machine. Skylake alone, with its 10% performance bump, isn't worth it. Polaris might be for some uses - I'd want to see how much it accelerates Photoshop and Lightroom... What I'd want to see is some combination of screen (resolution, gamut or both) and improved limits on RAM and SSD.
I'd love an improved keyboard, but the one on the Retina MBP is already pretty good. The latest Magic Keyboard is significantly better, and might fit in a laptop. The MacBook keyboard would be a major minus (although the same switches in the iPad Pro keyboard actually aren't awful - I'm not sure what the difference is, but the iPad Pro keyboard has more travel).
