The next question becomes: what possible protections could a WH alliance have against such an attack (or is there anything CCP should change to mitigate the math on such an attack---for one thing, it's a little odd that you can make a freighter un-attackable by logging out with its pilot, squirreling those assets away in-game indefinitely; maybe the balance of power needs to be changed on how freighters warp out at logoff?)
It's actually pretty hard to seed such a big ship in a wormhole, which is why they had to time it for when HK had a small presence. People that live in wormholes tend to obsessively dscan (kind of like a medium-distance radar that lets you see when ships are somewhere nearby you) and rapidly scan down new signatures (which can be PVE sites or new wormholes that people could be bringing things through). On top of that, big ships like freighters are slow to warp and hence quite susceptible to being caught on the way in.
In the freighter example, in order to safe logoff as you describe one has to be uncloaked and relatively stationary (ie: not warping around) for 60s (longer if they've attacked or been attacked recently). This is quite a vulnerable time for such a large (and hence easily scannable) ship. A well skilled player in a well specced ship (like most higher-level wormhole players will be and have) can scan down, warp to, and attack (giving a 15 min logoff timer) such a big ship well within that 60s if they are paying attention.
Removing the option for people to safe logoff in dangerous space would heavily discourage exploration of basically anywhere outside of high-sec which, imo, is where the majority of interesting content in the game is.
Still, it's a hair-raising 60 seconds. ;)
It's a game of cat and mouse, where the mouse can sit afk with a cloak on for however long they like until they think the cat is bored or not paying attention. Also worth noting another trick if you have reliable internet is to stay afk cloaked until the daily downtime logs you off. This way it's impossible to be scanned down because everyone gets kicked from the server at the same time.