μ is used a fair bit by anyone who uses the metric system, so it makes sense to include it. It's used as a prefix to denote a millionth for those that don't know, as in µm = micrometer = a millionth of a meter.

It's mapped to Alt-Gr+M on Swedish keyboards as well, but I've never seen a keyboard where it's actually written on out on the key.

> A fair bit by anyone who uses the metric system?

I'm sorry, but what?

Most people who use the metric system can't tell you which is smaller: micro or milli. Most people will never encounter anything in their lifetime they will actually need to reason about in some important manner that is measured in μ-anything.

As a user of the Icelandic layout I wasn't even aware that the key was on there, but I can confirm that we absolutely don't need it. I think there are probably a lot of keyboard layouts that could use modernizing wrt. how they are actually used today.

µ would be used by scientists, engineers, doctors and nurses.

That doesn't seem unreasonable, when we have <, >, { and } for mathematics, \ originally for logicians (to combine to make /\ AND and \/ OR) and |, @, _ and # for programming.

Shifted semicolon is absolutely a non-issue. If there are any problems with the layout, it's hiding the symbols behind altgr, but the shifted semicolon is really not a problem.

I think if my mother tongue wasn't English, and I therefore regularly typed on a different European layout, I'd remap the left Windows key or maybe Caps Lock to be an additional AltGr.