My only problem with that is that you have to be looking right at the phone when it goes off, or you're going to miss it. The current Accessibility feature for the flash only goes off once (at the time a notification comes in). It does NOT repeat.
Now, if you're meaning that the flashlight could stay ON/Flashing, at say some sort of reduced brightness, that MIGHT be workable. But you'd need to have more than one 'flashlight' led if you have multiple notifications. And I'm saying a reduced brightness, because to have one or three or more 'flashlight' LEDs lit at full brightness I think would hit the battery pretty hard over time. Not to mention being very distracting.
Apple could introduce some smaller, less intense LEDs - but then we're back to something Apple would NOT do.
And none of it matters if you lay your phone down on it's back (if you're like me, which most people aren't).