I have a couple of plants in my shallot patch which look like a cross with a wild allium, maybe the same one Allium canadense. They have flat leaves, which sets them apart from the shallots, paler and almost a lime green in color, and very small shoots in a very dense tuft. One is very dwarf and bore no seeds, while the other was larger and produced a few seeds from mostly incomplete flowers. We don't have wild alliums here, but the seeds came from somewhere in Canada and maybe some wild pollen crossed into her shallot patch. I plan to move them in spring, and I will be on the lookout for any deep bulbs - this could be a big advantage for us since shallow planted shallots don't do well planted in the fall. Besides, now that I read what you think of them, I'm hoping they would be tasty.

Anyway, a different type of bulb belowground would confirm it was some kind of cross.
I've also tried to get seeds from my Egyptian Onions but nothing came of it.
Incidentally, there is another cross of A cepa and A fistulosum on the market, called "Guardsman". It originated in the UK but is widely available in the US at present.
I will post a couple of pics of the tiny 'tuft', certainly looks "yellow-green", flower buds light brown and shaped like the shallot buds, flowers reduced and mostly petals - this pic from the larger of the two plants but they were basically the same only smaller on the teeny tuft. If anyone recognizes the likely parent of this, I'd love to know.