The Supreme Court ruled unanimously Monday that states may use total populations in drawing districts. The slip opinion Evenwel v. Texas is here. The Washington Post has a story by Robert Barnes here.
Conservatives have generally wanted to count only voting age people, and have objected to “one person one vote”. Democrats have favored allowing more people to count because they tend to be larger families who may be more likely to support Democratic (especially Bernie Sanders-like) policies. But there is also a philosophical question: should families with more children actually have more votes or more representation? (The inverse of this was the slavery-era 3/5 rule.)
In the late 1990s, proportional representation as a topic of debate among libertarians, and is covered in my 1998 “Our Fundamental Rights” booklet.