You're correct, I meant not upgradable. At least not upgradeable and maintain a warranty and there still aren't any compelling upgrades. What am I going to do swap in a newer 750GB SSD module?
To digress a bit...
In the days of hard drives, going SSD or hybrid SSD was compelling because it gave your old computer a new life, possibly better than new, but sitting at 750GB and 16GB of RAM a mid-2012 Retina MacBook Pro and I have trouble justifying a 'need' to upgrade. The performance is still quite good. My official work 2015 rMBP just sits in its bag, solely because I prefer the US keyboard over the International English one, although the 2015 is faster.
On some level, I'd like 32GB of RAM and 2TB, but as a developer I also see that we've sort of hit peak requirements on this type of spec. The big change in the macOS/iOS system has been the movement of the disk pigs to the cloud. The move of Music and video to 'the cloud' stopped rapid disk usage growth, then iPhotos library further slowed growth, and now Documents and desktop clutter moving to iCloud has actually cause usage to shrink. GitHub also helped to some extent in allowing me to blow away all those projects I was keeping around out of nostalgia. So, from my viewpoint anything over 1TB local storage is just an inability to accept that the disk is for local caching and current work. RAM is also not a problem, 16GB is fine, although 32GB would be future proof it wouldn't be worth going with non LP RAM given the context of this article.