I found this map on PDOT's website (
see this link for the Streetcar System Plan - the map is under "Draft Primary Transit Index Exhibit").
I think that's probably where the Oregonian got the map shown in NJD's post above. This one doesn't say that these are potential streetcar routes, but just that they (the red lines) are "1st Level PTI." PTI = Primary Transit Index, which apparently is just a high demand transit corridor. Some of these could end up with streetcar lines, but I doubt the city is anticipating all of them. But we probably knew that. Sorry if this map or the link has been posted before.