Proportional representation based on race or ethnicity is a profoundly evil idea to me, that makes my skin crawl.
How about based on party?
I don't know that I like the system it inevitably creates. Multiple parties to represent the different parts of society rather than two big tent parties is obviously a huge plus. The downsides are twofold; a political system prone to huge swings, exacerbating rather than moderating economic or societal problems (as can be seen, for example, in Greece) and an inevitable strict party line, meaning all independent voices in government are shut out.
It may not be as bad as you think. From 1870 to 1980 IL used a modified cumulative voting system to elect its lower chamber. There were three house seats per district and partisan proportionality was roughly followed by offering each voter three votes to cast including multiple votes on a single candidate. It arguably produced less partisan results than the current single member system. It was only discarded during public anger over a pay hike for legislators in 1978.
Yes, I remember that system when I was at the U of C, and quite liked it. Among other things, the few Pubs in my assembly district in Hyde Park were heavily romanced. I mean if you are one of about 300 Pubs, and can elect someone, suddenly you become rather important. We quite enjoyed the attention.
It does stack the deck in favor of moderation, no doubt about it.
However, as I remember the system, the minority party in each district elected one guy, and the majority party two guys. If it was just cumulative voting, then no Pub would have been elected from Hyde Park of course.