My own guess list …
Reuven Carlyle seems very likely. Carlyle is very ambitious, has some personal wealth, and is a policy wonk with a tech background that fits Seattle’s Zonians.
I am not so sure about Dow Constantine, Dow has been mentioned but he is more of a governing wonk than a legislative blow hard.
I would, however not be surprised if Mayor Murry or some other Councilman (Licata or Burgess?) take the plunge. Murry is a long time legislator who has badly wanted this job. He has gained a huge amount of credit as Mayor but as Congressman, this would be a life time job!
Licata is the real liberal on the Council .. or was until he chose not to run. Burgess is very bright and would get great support from the business community .. including, I suspect the corporate liberal who make up Seattle’s uber wealthy elites.
Sawant? Seattle’s messianic socialist REALLY wants this. She lives in Leschi just outside CD 7, but that is not so much a big deal for Sawant. She has huge financial resources so buying a condo would not be much of a challenge for her patrons in the SEIU. I hope she runs. She would be iced and diced.
Mike McGinn or Nick Licata are more viable as progressive candidates and wither one would make a reral contest with Reuven.
Gael Tarleton has also floated her name. This would be interesting for a number of reasons. She is pretty much embedded in the Democratic/liberal Seattle establishment and, based on some of what she has written on FB, might run as the only female Democrat candidate.
Gael might find other opponents for that title, e.g. Jenny Durkan. Then there is the ambitious Courtney Gregoire, scion of the Chris Gregoire clan. I doubt the younger Gregoire is satisfied as a Port Commissioner.
Other names are too many …. Eric Liu, Mike McGinn, C.R. Douglas, Bill Bryant, Hilary Franz, and Rick Steves.
Ross Hunter has been mentioned on the conservative side but I do not think he lives in the District. That said, I would not rule out a libertarian Republican. Imagine the effect of a a few bucks from Bezos or Balmer backing their kind of candidate?
Another possibility is a non politician .. a techie. Seattle has a huge number of very bright, very wealthy, somewhat retired tech types who might see this as very much.
The question I have is how important is the Democratic party in Seattle? The party’s resources in District 7 were greatly amputated when redistricting cut the District away from its traditional low income, labor union roots. It is not hard to imagine a candidate running on resources outside the DP ..whether that is a more national source, like Sawant’s “Socialist Alternative Party” or Nick Hanauer’s vanity effort or the Koch brothers.