Some of the most logical light rail routes are outside Phoenix city limits. The one that would make the most sense by far is a Scottsdale Rd / Rural Rd route running north-south through Scottsdale, Tempe, and Chandler. Of course, that's not going to happen due to Scottsdale's obstinance.
That unrealized dream aside, there's currently an
Arizona Avenue Alternatives Analysis in progress, focusing on another corridor in Chandler. The "locally preferred alternative" is supposed to be presented in December 2020, which means any day now. It could be light rail, but it could also be a revival of BRT along that corridor or perhaps a streetcar. The light rail or streetcar options will be controversial and I give them a 50/50 chance of approval.
The Alhambra / Glendale route that was scuttled made sense until it reached downtown Glendale. The Glendale City Council foolishly saw Westgate as the ultimate destination, but the sports sprawl there is always a team relocation away from irrelevance. A cheaper and much more sensible option would have been to head north along 59th Avnue from downtown Glendale, serving destinations like Glendale Community College along the way. Unfortunately, that was never seriously considered.
Unless Chandler comes on board, I think we'll ultimately end up with a system map much like MARTA in Atlanta, which does a good job of serving the central city and selected inner suburbs but does not serve the entire metropolitan area. I'm okay with that because the areas that have embraced light rail are the ones I most often visit. Still, there may always be a sense of what could have been.