Well, the final count for WA isn't over - however at this point the projections show that it won't be defeated. Everyone is reporting it as a win for gay rights.
Daily Kos: Marriage Equality called for Washington State
"With 60 percent of the vote counted, R74 already has the support of 65% of King County and is performing well in key Eastern Washington counties. Simply put, it’s now impossible for opponents to overcome the 52-48% spread for R74."
Absolutely we can expect opposition. However, with Obama in his second term and without re-election worries, we may find him more supportive of legalization than in times past.
The other thing to consider is how alcohol prohibition was finally defeated. I believe there were 26 states with various alcohol laws of their own passed before the federal government finally relented and prohibition ended.
At this point, there are 18 or 19 states with cannabis legalized either medically or fully or decriminalized. Cannabis has already been available to medical users in Washington State, although there has been extensive push-back from the feds, with dispensaries being shut down left and right. Collective farming is technically allowed under the provisions of the medical laws, and has been going on legally for some time now in King and Spokane counties (there was one remaining collective in Spokane until a month ago, when he closed down voluntarily because he has purchased a license to sell under the new law, which will treat cannabis in a manner similar to alcohol).