Ken would have to notify any other registered parties that Ukyo owes money to about this sale of the assets, and would have to distribute any proceeds over and above what is owed to them.
We are in a grey area as you have indicated. Little in the BTC industry operates within the letter of the law as it is currently written.
The action Ken is taking is within the spirit of the law - that which is the underlying intention. That intention is that an individual or company can hold the assets of a debtor and sell them to recover their losses if the debtor does not or can not pay up. That is as far as you can go.
You are implying that Ukyo could take Ken to court but what legislation would
he use? The shares he will claim to own are not registered securities, the BTC he used to buy them is not a legally recognised currency, the exchange he set up was not registered etc etc. Do you see the problem? In other words if Ken can't do X because the legislation does not appply then Ukyo cannot do Y (bring him to court) because the legislation does not apply.
At the end of the day common sense needs to be applied in any Grey Area. So I would maintain that Ken is doing the right thing.
Actually, it isn't in the spirit of the law. Construction liens and garage owners liens are designed to protect tradesmen who invest time, materials and money into your house/car/etc. If they do that and you don't pay them for the work, they are able to put a lien on that item. Even then, there are specific ways they have to go about resolving the lien. If you don't pay your roofer he can't put a lien on your car or cottage, and a garage owner can't put a lien on your house if he worked on your car. If you refuse to pay your roofer after you get shingles installed and he takes your car until you pay him, both he and everyone else who might be owed money on the car have every reason to go after you.
I have no idea what sort of corporation/LLC/entity Ukyo's businesses were registered as, but Ken seizing and selling the ActM shares to cover the We-Ex debt, besides being somewhat morally suspect, is almost certainly not legal.