RD<
I don’t see were you mention shellfish above. You go out of your way to say that swwordfish and sturgeon are not a problem and therefore one would have few issues eating from such a kitchen. Which you reiterate again below with out substantiation. There are numerous issues that ylu have not deallt with. And a number of you assumptions are no more than just that, assumptions about what may be in that kitchen.
As an aside, whay do you only *try* to be makpid on yoshon if you feel that is a deoraisa?
If it is because you believe that yoshon does not apply to chuts laaretz, then hakpadah on it is even less apllicable than cholov yisroel which certainly applies. R Moshe must have held that American milk is not the same as cholov yisroel because a) he was makpid on it himself and b0 he told yeshivos that they should spend the extra money it costs to provide cholov yisroel.