Remember that you can hold on to the property for 3 additional years after moving and still get the 500K Federal Tax Free gains when selling.
https://www.investopedia.com/ask/answers/06/capitalgainhomesale.asp"The 2-in-5-Year Rule
For taxpayers with more than one home, a key point is determining which is the primary residence. The IRS allows the exclusion on only one’s primary residence, but there is some leeway in just which home qualifies. The two-in-five-year rule comes into play. Simply put, this means that during the previous five years, if you lived in a home for a total of two years, or 730 days, that can qualify as your primary residence. The 24 months do not have to be in a particular block of time. However, for married taxpayers filing jointly, each spouse must meet the rule."
If you are holding, this would effective be a bet that Seattle SFH would appreciate at a higher rate than however you choose to invest the equity from a potential sale.
Also, note that the Fed has already said they will increase interest rates multiple times in the next year. Over time, this will decrease the amount that folks can afford to pay for their homes.
Whatever year you decide to sell, make sure to place it in the market in the late spring April/May when housing demand is highest.