Just an update
Now I know this isn't a question asked a lot. but I had the same question and found the answer you're looking for (which is different than stated)
The SSD drive is NOT soldered and IS quite replaceable.
Follow the instructions here to replace it (I don't see much about WHAT KIND of ssd drive you can use) but you'll be able to figure out HOW to do it here:
In THIS video the guy is showing you how to "reseat your drive" ignore that part because he shows you exactly how to open it up (and you get to see everything you need not only to "reseat your drive" but also how to replace it if you wish to do so.
Has anyone done it? I bought mine for $30 a week ago and it's running ChrUbuntu with the chromeOS still intact (I think I should just wipe away the chromeos)
Here's the how to. installing 12.04 (which I know is two years old know) at least lets you "upgrade" to the latest apps.
Chromebooks and Chrome OS: ChrUbuntu 12.04. Now with double the bits!
It says on Ubuntu 12.04.5 LTS BUT all the apps (like chrome browser) and everything else update very nicely.
Giving you a VERY capable, and perfectly fast laptop (which I just leave in the car for when I need a laptop with 6 hours of batter life ;-)
It even has a GSM modem on it and if I can just convince T-mobile that it's a "tablet" they'll give me 200Mb/month free (and a small charge if I go over it)