Currently, Both SEA 330/350 FO's are senior to 64% overall seniority. It's the most senior WB base right now. SEA 350 Opened in June, so it may be a little senior to what it will be in future years as we take more deliveries, and Asia builds destinations.

All that said with known retirements and no growth, you are looking at 12 years to reach 65%. With 2% growth, that would drop to about 8 years (end of 2033). Obviously, if the awards get more junior, that will shorten that timeline to an unknowable degree. I give zero chance of a NH getting a WB in the foreseeable future, if not ever. If it helps, there is a fair amount of history and data available here.

Getting a NB out of SEA is possible, if not on the initial award, relatively shortly via a base change. Many NH's have good luck swapping bases very quickly. No guarantees.