You'll have more luck pushing for this by developing a multisig wallet implementation and getting people to actually use it first - P2SH required a painful soft-fork yet years later it's still hardly ever used, making people question the value of new features. P2SH was something that everyone was supposed to be using by now because of the "obvious" security need; you're proposed reason for a soft-fork and associated system-wide risk is significantly more niche.
Slightly off-topic, but if it wasn't for the rapid blockchain growth and my procrastination in fixing Armory's scalability issues, I'd have Multisig-with-P2SH implemented already. The problem is not the features being useless or unwanted, it's that there's such a shortage of human capital to make progress in this part of the Bitcoin development world. There's so few environments where such a feature could be implemented, and so many other priorities of the few people developing those environments.
However, this particular change is trivial to implement, and dramtically simplifies implementation of any kind of offline signing device. There's no doubt it would be used immediately by Armory and all the HW wallet developers.