The stop of all your skill (expecially if towers are not affected) is not a big drawback, couse you can simply use all them BEFORE you play that card.
Other than that, the only skill that applies on YOUR turn is Immortality, so there is not point to make a card to shut down them all (you can simply make a card that shouts down immortality, if that is the idea.).
And, anyway, I think immortality shoul remain as it is...
There are yet shields to manage them (even kill or stop them, like fire, frost and time shield), I think that is enough...
Immortal creatures are expansive and not very strong to balance their immortality, if they can be targetted, they will need a buff...