US News had the story in 2012 (Elizabeth Warren's Quiet Support for Public School Vouchers), and it comes up again in the latest New Yorker as part of a review of her new book (Reading Elizabeth Warren).
Warren doesn't just support vouchers in special circumstances, like special education placements or DCPS. She wants to give them to everyone, everwhere.
As quoted in the New Yorker piece, Warren has written that
“An all-voucher system would be a shock to the educational system, but the shakeout might be just what the system needs.”
According to Warren, those "public" schools in expensive enclaves aren't really all that public as their defenders like to make them sound:
"Schools in middle-class neighborhoods may be labeled 'public,' but parents have paid for tuition by purchasing a $175,000 home within a carefully selected school district."
Interestingly, Warren's argument is at least partly based on the high housing costs associated with the current zip code-based system of allocating scarce quality schooling. High housing costs, plus burdens on working Americans (mothers in particular) have been a scourge for decades, according to Warren. Breaking the link between housing and school quality would relieve pressure on families that have moved to expensive places just for the schools.
Warren's ideas have been debated on Diane Ravitch's site in recent days -- they're New Yorker readers too, it seems :-) -- though not surprisingly the idea is being met with shock and disappointment. And the New Yorker writer, Jill Lepore, calls Warren's proposal reckless.
*Correctification: Though she uses the term "voucher," which is commonly used to denote programs that include private and parochial schools, Warren is primarily focused on eliminating the link between neighborhoods and public school assignment. The 2012 US News article cited above calls Warren's proposal "public school vouchers." The original 2007 proposal excerpted by AFT Kombiz uses the same language (though it doesn't specificaly exclude private schools as I read it). "The public-versus-private competition misses the central point," writes Warren. "The problem is not vouchers; the problem is parental choice."