Installing and running Arch linux on the new MacBook 2015

Question

So Apple has just started taking orders for the new 2015 MacBook. You know --
the thinnest and lightest MacBook to date (even thinner than the MacBook Air),
with a 12 inch retina display, the Intel Core M processor, a single USB-C port,
and the new force touch trackpad.
I'm pretty sure there are a few people like me who'd like to buy this new
MacBook and then install and run Arch (or some other flavor of linux) on it.
But of course, this MacBook is in many ways very dissimilar to previous MacBook
Pros and MacBook Airs. So this thread is a shout out to likeminded individuals
who are willing to brave the odds and install Linux on this new machine, so we
can help each other figure out (and hopefully fix) the inevitable issues that
will arise when we venture into this uncharted territory!
I have a little bit of experience installing and running Arch on MacBook Pros
and other Apple computers, but I'm (very) far from being an expert. But based
on my limited experience, I think the following areas will pose the biggest
challenges to getting Linux properly up and running on the new MacBook:
1. Installation: it's possible that booting a live USB will fail. So we might
   have to use a CD. Indeed, perhaps we may even have to build a special ISO
   image for this laptop. And once the install is complete, EFI/EFISTUB booting
   with/without refit/refind may or may not work. Also, installing a bootloader
   (grub, gummiboot, etc.) for dual booting Mac OS X and Linux may be a
   challenge. We might have to endure kernel panics and deal with cryptic error
   messages while booting.
2. Wifi may or may not work reliably. We might have to do some tinkering with
   different drivers, etc.
3. Battery life may not be very good. We might have to fix a few things here.
4. The HiDPI retina display may or may not work properly with specific window
   managers/desktop environments. Fonts/icons might be too tiny, may not scale,
   etc.
5. The new Force touch trackpad may not work out of the box. In fact, I'm
   fairly sure the regular xf86-input-synaptics package won't play nice with
   this trackpad. There may not be support for features like the trackpad's
   haptic feedback, multi-finger gestures, pressure sensitivity, etc. Indeed,
   this might actually take a while to get properly working under Linux.
6. I don't know if the new USB-C port will work out of the box. It may not
   play nice with USB flash drives and other peripherals and there may be
   issues with ehci/uhci/whatever.
I tried Googling around trying to learn as much as I could about the issues
above, but since the laptop is going on sale only today and most users are
probably not interested in running Linux on it, I came up quite empty. I think
many others on this forum might also have faced the same issue.
So here's an open invitation. Let's share our experiences trying to get linux
working on this laptop. If you buy this laptop and try to install Arch on
it, please let us know how it went! Even if some things work out of the box, it
might be useful for others to know, so please share.
And of course, if you have more information/gotchas: for example, if you
encountered and managed to fix one or more of the issues above, or you
encountered a problem that's not on the list above, or even if you tried
something and it didn't work out as expected, please post below. I'm sure this
will be a very big help to others trying to solve similar issues on the same
hardware. Thanks!

Answer 1

It would probably be beneficial to post the output of lsusb -vvvv and dmesg. 
FS1RTG77 wrote:
2. Broadcom BCM4360 AirPort Extreme, not supported.
5. The new Force touch trackpad and keyboard, both SPI bus devices, do not work.
On 2, it may just be a case of needing firmware, my laptop has a BCM43602 card, and the firmware required has only just been added to the linux-firmware package.  Prior to that I had to install it manually.
On 5, I'm wondering if you identified them as SPI devices by looking in OS X, I ask because my laptop categorises my keyboard and trackpad in the same way.  But they are actually still both connected to the USB bus, and presumably using SPI as an interconnect between the keyboard/trackpad and the microcontroller that tie them together.