I'm always a little hesitant to change something existing like that. Most of the various mez effects are doubled up on as far as sources from Alpha goes (excluding I think confuse and fear), and changing that little thing would lock people into Resilient if they wanted to also increase their Immob slotting. Generally, I prefer more options, not less, although I don't think it'd be too big an ask to put it on Musc Radial Paragon. But then, you get into this would break the setup currently held to by everything in Alpha. (Radial Paragon = 6 lesser bonuses, Core Paragon = 1 bigger bonuses, 2 smaller bonuses).
I agree Interrupt probably doesn't need it, as at most you'd have like, 1 power that benefits from it? But then that also holds true for Fear and Confuse, and at least they get some representation.