The talk of Scandinavia as an example is very interesting given recent events in Sweden, which is largely going the same way as Germany, if not worse, after also taking an unwisely large number of immigrants and refugees in very quickly. Taking a very large number in a short space of time seems to be problematic.
On quotas, lets think about how it would work in a practical sense.
A common one spoken about lately is old white men on boards. So lets set a quota then.
The argument is too many old white men, so the quota has to limit them. We can't define just by white though, that's not a race. How do we set the bar? What if someone is one quarter Maori but their skin is white? Do we have to agree a fraction that is allowed, and then prove our ancestral make-up on a case-by-case basis? What countries qualify as white? As you travel around the Mediterranean, or up the Americas, where does the skin colour officially cross from white to non-white? Plus places that have had white people settle on them later, like here, SA, Australia, USA, Canada, do you have to check the family history and see if they are from the "white" countries?
That's getting a bit tough to do.
So do we reverse the formula? Make it X amount of females? But then what about Old White females? Young White females? We've got the same issue with race, we have to split everything into sub-categories, and we haven't even started on gender. If we're limiting males by setting a quota for females then it's only truly equal if we bring transgender people into the mix. Doing it from this direction turns out to be just as difficult.
Unless these quotas are done properly we're just cherry-picking, and whichever minority is not getting a quota is being discriminated against. You cannot allow for everything. Quotas are simply impractical without discrimination.