There's absolutely no requirement or testing that says your portable device can't interfere with an ILS. Landing on instruments in zero visibility with untested consumer electronics that don't conform to aviation specs is a bad idea. Maybe it's time to change the regs so anything that can go on a plane has to be tested and regulated to not interfere with aircraft navigation.
When PCs came out, they interfered with TV. There's a set of standards for consumer equipment, eg won't interfere with your neighbor's TV, and a set of standards for aviation, eg won't interfere with an instrument landing system etc. And even if in the current crop of digital devices, it's a low-percentage problem, new devices get invented all the time, with new power and frequency profiles. There is so much change that eventually something is guaranteed to interfere.
In any event, the reg about no cell phones on during flight (as opposed to no electronics during takeoff and landing), is an FCC reg, not an FAA reg, to help out the cell phone companies not having to deal with fast-moving cell phones on max power talking to all their towers at once.
I haven't seen any studies that guarantee the safety of wearing cotton clothing or rubber shoes, both of which have vague effects on electromagnetism as well. Not having any evidence that it's unsafe is good enough in my book. We've had a couple of decades and millions of flights where passengers forgot/ignored/didn't understand the rules without causing a single incident.
Why ignore the evidence? Electronics are not being turned off, which means thousands of flights per day have been made for years with electronics on. Apparently there has been no incident serious enough to up the risk beyond "not guaranteed to be safe". Could you possibly fund a more extensive test of the danger than what is already happening?
The public should be asked if they want to waste many billions, if not hundreds of billions of dollars in lost work to mitigate this "risk".
Frankly, nearly anything is possible if you're accounting for the unknown, like you seem to be doing. Perhaps we should also ban prayer – after all, there may be a god, right?
The FAA does not ask, "are electronics likely to cause a crash?". Instead, they ask, "can we guarantee that electronics will not cause a crash?".
There is a big difference between claiming that something is dangerous vs claiming that something is not guaranteed to be safe.