So while I wait for the 2016 iteration of the 12" MB to finally appear, I've been thinking about whether this would be a suitable primary machine or not.
My 2011 27" iMac is my primary machine right now, but it's close to 5 years old, and since it's stock, it has a spinning HDD inside. I was thinking of getting a 512GB version of the MB because of the possibility of my iMac's HDD dying suddenly.
I don't do anything that would severely tax a Mac. Most of the time, I have a bunch of Safari tabs along with Word or Nisus Writer open doing translations. I have an external drive for my music needs. As far as entertainment is concerned, I play games, but they're all really old games; my current obsession is Diablo II, followed up by emulation of 8 and 16-bit consoles.
Other than a much smaller screen size, would the MB be a suitable-enough primary machine?
I use it as my primary machine. It wasn't my intention to do so, but last year my plan to also buy a riMac fell by the wayside due of some unexpected expenses.
My usage isn't heavy--writing, freelance editing, surfing etc. I found the machine quite sluggish at first, but El Capitan solved many of those problems. My chief difficulty is when I'm editing large documents and accumulate around 1000 tracked changes (in either Pages or Word), my CPU usage goes through the roof and the app becomes laggy. With a desktop, I wouldn't even really worry about this because I would probably be doing most of my editing on the larger machine, but it does get annoying on this one. I should say also that I've had this problems on other kinds of machines too--including PCs, and Android phones. Strangely, my iOS devices (iPad Air 2 and iPhone 6S+) manage these exact same documents without any lag. I'm curious to find out what exactly causes this lag. Even now, though, because I take this machine with me everywhere I go, its portability trumps this hassle. This thing weighs the same as my first iPad did. That's phenomenal to me. I don't even notice it in my bag. And it is so portable I'm not even totally sure why I have an iPad still, tbh (I do find my iPad useful when I'm teaching, but the MacBook would do just as well if I wanted it to).
I would not worry about the smaller screen (unless of course you're comparing to a 15", but that's apples and oranges). The aspect ratio on the rMB is far superior to the rest of the MacBook lines. I find I actually have more usable space on the 12" screen than I do on a 13" rMBP.
I also cannot say how much of a relief not having a fan is. When writing, I find fans to be horridly distracting and I'm glad to have it gone.
I have no qualms about the keyboard either. I fly on this thing. I've been whining about wanting a keyboard like this for years and now I have it and I love it. I have found it's especially prone to debris under the keys though--even a little bit can cause you problems, so you have to be careful.
Battery is not bad also. Generally I never run out of battery during an 8 hour work day, but sometimes its close (especially if I watch Netflix over lunch). It's a good battery, but it's a close call somedays if it'll need a charge before the end of the day and I'd rather not have that on the back of mined (I petulantly refuse to carry the charger because that to me seems to defeat the purpose of the portability).
I'm curious to see what Skylake will bring. It might solve problem with large complex documents and bring the battery around the turn. I won't upgrade though. I'd rather spend my money on a new iMac. I anticipate upgrading this rMB at the end of my Apple Care, I expect.
