In the for what it's worth department, any sub with 53cm tubes is now a nuclear missile sub according to your link and your argument.
All one has to do is get one's hands on a nuclear tipped missile or torp that fits the tube ...
With that in mind, the next time any nation's submarines deploys, they have deployed a Nuclear Missile Sub.
Which, when I think of it, is a pretty dishonest way of describing things.
The no-kidding nuclear missile subs, carrying SLBM's (Delta III's, Ohio Class, Vanguard class) are a much different kettle of fish than subs carrying cruise missiles ... that may or may not have a nuclear payload.
Cruise missiles can be defended against with conventional air defense, albeit EW is very handy.
Ballistic missiles? No.
Compare TLAM (N) (Tomahawk with a nuclear payload) and SS-N-21 (Russian cruise missile with a 200 kilo ton warhead) with a Polaris.
Small wonder the US and Soviets, in the 80's, wrestled with the arms race implications of cruise missiles with nuclear tips.