It looks like there's a better than 50/50 chance we'll get a ballot proposal on this coming November. See p. 28 (of the report, p. 31 of the pdf):
http://www.nyc.gov/html/charter/downloads/pdf/preliminary_report_final.pdf
To start it's only for nominations, but that's a big start in an often one-party town. And the start is the hardest hurdle. If it works there, getting it extended should be easier. Cool!
Michael