Agreed there's nothing in the data to directly suggest government involvement.
It's only "sloppy," though, when conceptualized as a MITM. China does have an extensive history of censoring access to sites, and recently censored access to GitHub entirely IIRC. It could be that they decided to block SSL access, but allow HTTP access, and this is how they implemented that.
Everything in my bones (25 years, 中文研究, China research) tells me the China government is directly involved with this. China is corrupt beyond belief, and any smaller destabilization can lead to further problems.
I agree that this may be a further extending of the "New Years train ticket" block on Github.
It may also be new toying after the recent "experiment". Leaving Github without SSL inside China still makes trouble - China's insidious corruption at the very top is subtle, incremental small steps, all designed for the "long game".
It may also be raw mercantilism ... as with Google, Twitter, and Facebook long before this.
As an sort of old china hand, china is corrupt but not beyond belief, there are plenty of countries that are much more corrupt, even India is worse than china and they even have democracy.
The level of sophistication that the GFW seems to be achieving is disturbing. We've had certificate attacks before, perhaps they are testing something out that will be deployed more broadly to solve there "gmail" problem?
SSL infrastructure was already known to be best treated as globally compromised.
If this is real, then the Chinese may have collected some interesting statistics regarding the percentage of developers who don't care about certificate issues.
I didn't see the cert appear over the wire myself, but I'm in China at the moment and spent part of this week in communication with the Gentoo and Debian release engineering teams suggesting they revisit perceived issues in their respective key distribution processes and documentation (issues focused on automated validation of install media; not individual packages). Gentoo was already working on it and Debian got back to me pretty quick. I don't feel I was wasting my time now.
Really, we need a key distribution and trust anchor solution for the masses, as Moxie has spoken about, that includes 'trust agility'. IIRC the latest iteration of his proposed solution there is http://tack.io/
It's worth pointing out that many governments have MITM and warrantless surveillance systems, not only the Chinese. For more background see http://wikileaks.org/spyfiles/ which summarizes "Mass interception of entire populations is not only a reality, it is a secret new industry spanning 25 countries." and Jacob Applebaum's keynote at 29C3, https://www.youtube.com/watch?v=QNsePZj_Yks (Youtube is also banned in China).
(edit: posted beneath this thread as moxie is one of the community's most respected parties in this area and just posted, but had some extra info in here! :)