The Washington Supreme Court decision is excellent and well-reasoned, but it has some dicey prospects looking forward.
If it comes before the current eight-member US Supreme Court, it might be affirmed. The odds fade if the Senate confirms Trump's appointee Judge Gorsuch to fill the current vacancy on the Court.
Gorsuch is a fervent advocate of the idea that the "religious liberty" of fundamentalist Christian business owners should override rights of women or LGBT people. That's what his opinion was in Hobby Lobby v. Sebelius when he weighed in on it at the appellate court level. The citation is 723 F.3d 1114 (2013) if anybody feels motivated to read Gorsuch's detailed concurring opinion.
The Hobby Lobby decision allowed a corporation controlled by right-wing fundamentalists to strip contraception coverage out of the health insurance provided to female employees, despite the fact that federal law required health insurance plans to cover contraception. The corporate owners resented the fact that their female employees would have access to contraception that the owners found religiously offensive. Gorsuch said the owners were in the right, and that their religious concern outweighed the government's interest in regulating health insurance to ensure that women have access to contraception.
Given his reasoning in Hobby Lobby, there's no doubt that if Gorsuch gets a chance to review the Washington Supreme Court decision his opinion will be that the "religious freedom" of business owners should outweigh the state's interest in protecting LGBT people from discrimination in public accommodations and the provision of ordinary business services to the general public.
Under this banner of "restoring religious freedom," the House of Representatives is currently considering legislation to allow business owners to evade compliance with anti-discrimination law. Donald Trump has pledged repeatedly (both before and after the election) to sign such a bill if Congress passes it.
If events develop along this line, we may soon see signs in shop windows saying, "This is a Christian store. We don't serve gay people." Or interracial couples. Or Mexicans. Or Jews. Or Muslims. Or you-name-it. Would this be used against transgender people? You can bet on it.