I finally found the holy grail.
That's right. An LED bulb that works in an over-the-range microwave.
Though I love LED bulbs for the energy savings, in this application, it's more than saving a few bucks in electricity. They just burn out all the time. It seems like literally every single month I have to change a bulb in the microwave. Apart from the fact that Home Depot gouges you for 4 bucks a pop for these replacement T8 bulbs for microwaves, it's annoying to keep changing it. I have longed for an LED replacement for longevity.
Here it is, in all it's raw glory. I ordered this straight from China, since in the US, apparently there is a conspiracy to ensure a steady stream of T8 bulb sales, and there is no such product available.
While this particular bit of nascent imported technology doesn't seem to have a name, your crucial search criteria on Ebay are E17 LED (the base is E17). It is easy enough to tell by the pictures on ebay if the bulb is going to fit in a microwave. The ones I got were about $3.50 apiece shipped... less than a conventional 30-day-life-expectancy bulb.