The major TLDs (.com, .net, etc) are relatively safe, since any changes would likely be difficult to get through - with any changes quickly noticed ... as in within minutes, or even seconds; likely wouldn't even be that effective, since the most popular TLDs zone dns entries are heavily cached.
However, ccTLDs are a different story completely, since ccTLD zone name server changes are more common and thus such change requests would be far less scrutinized.
I've never heard of any TLD being hijacked, but could likely be easily done, since the social engineering involved would be very similar.
Changes to TLD nameservers need to pass human inspection at the IANA, human inspection at the US Department of Commerce, and human inspection at Verisign (who provide maintenance for the root zone). This is in stark contrast to the largely mechanical process by which domains in gTLD and ccTLD registries are modified.
Requests to change entire NS sets (as opposed to simply dropping a couple and adding a couple of other nameservers) are typically stalled early in the process while the IANA requests justification for why the entire set is being changed at once.
Hijacking a TLD would require a lot more social engineering than your note suggests.