What *should* be in there is entirely to taste, so long as it comes from a definitive list of acceptable ingredients (which has been discussed to death). I don't like tomatoes. Some people hate mushrooms. I'll only eat black pudding if it's the oaty, Scottish stuff and not the fatty Bury style. That's fine, so long as their replacements come from an accepted list. There's some arguing to be had (I like streaky bacon, but I don't think it belongs in the FEB), but I think we're fairly clear on what's OK. The closest thing to proper heresy I've seen here is that some people don't like tea.
What's more interesting to discuss is what *shouldn't* be in a Full English. Like omelettes, and chips. Not that an omelette with chips isn't a nice breakfast, but neither of the items have any place in a Full English. Or putting it all on something other than a fucking plate. Yes, I've eaten breakfast off a slate tile, and no I wasn't amused by it.