I was discussing sleeping bag temperature ratings with a few other engineers and the idea of an 'At Home' temperature rating test was brought up.
The idea would be to come up with a testing procedure that would be easily replicated by just about anyone at little or no cost ($15 for a thermometer, perhaps). We're thinking it may be possible to calibrate this test using the EN 13537 standard if we can get a few bags that use that rating to test.
If there's any interest in this, I'll put some effort into developing the idea a bit further. I happen to work in a sporting goods store that has a few EN rated bags on display that I think the boss will let me use for testing purposes, so I can do some of the calibration work myself. However, finding a few other folks with EN rated bags that would be willing to do the test as well and forward their results would let me further improve the accuracy.
This would allow DIYers to include a reasonably accurate temperature rating with their write-ups, since 'comfort' tends to be such a subjective thing.