I am aware. That "dozen or so" is a problem: when everything is an interrupt, there are no interrupts: it's just scheduling, and things that must be scheduled frequently can't suffer "a dozen or so" overhead. For the SRP model to really hum, you need the silicon that solves this.

I've found that it doesn't matter except for something that you want at the absolute highest priority anyway, which then by definition doesn't need to jump through the same hoops because nothing can preempt it anyway.