US Supreme Court upholds Washington Open Primaries
The US Supreme Court upheld Washington's system of Open Primaries on Wednesday, opening the door for a similar effort in Oregon to move forward.
An Open Primary, as defined in Washington law, and under a measure being promoted by former Oregon Secretaries of State, Phil Keisling and Norma Paulus, allows any voter to vote for any candidate in the primary election, and the top two candidates will advance to the general election.
The Open Primary system has been opposed by both major and minor political parties, that have argued that it limits free association and the right of parties to nominate their own candidates.
In its ruling, the Supreme Court pointed out that unlike previous forms of the Open Primary, the versions in Washington and Oregon do not prevent parties from selecting their own nominee independent of a state-sponsored primary.

The U.S. Supreme Court said
The U.S. Supreme Court said absolutely nothing about the system Keisling proposes for Oregon. Nothing at all.
Further, it is not correct to refer to either the Washington system or the Oregon proposal as an "open primary." The Oregon Supreme Court ruled that the Keisling proposal is not an "open primary" but is a "blanket primary." Big difference.l
Oregon and Washington "top two"
The Washington "top two" which the Supreme Court upheld is nearly identical to the proposed Oregon initiative. All candidates are listed on the same ballot, with the top two vote-getters, regardless of party, advancing to the runoff.
A party is free to nominate candidates by whatever method it chooses, in advance of the state-conducted election. But there is not a "party line" on the ensuing election ballot; there can be other candidates from the same party. Washington's 2 major parties will nominate candidates through a caucus/convention process.
Further litigation seems certain vis-a-vis the Washington "top two." The Supreme Court left the door open for an "as-applied" challenge after the system has been used once. And the system is unconstitutional as applied to congressional elections.
Oregon Measure Has No "Nomination" process for Major Parties
Yes, SCOTUS has recently disfavored facial constitutional challenges, and the Washington State Grange case was not dispositive, so it will be litigated "as applied," and the Libertarians can assert their trademark claim SCOTUS did not reach. Regardless of current WA law, it appears that the Oregon blanket primary eliminates any meaningful nomination process other than the blanket primary for the major political parties.
Under current OR law a major political party (Rs and Ds) may "nominate" only by state-run primary. ORS 248.007(7). Potential candidates for nomination by major political party must file either a petition or declaration with SoS. ORS ch. 249.
Sec 18 of the proposed measure maintains the current language of ORS 254.115(1)(c) which requires that the names of all those who have filed such petitions and declarations for major party nomination appear on the primary ballot, which would now be the blanket primary ballot. While Sec 9(2)(d) and (4) of the measure allow the notation of "endorsed by" next to a candidate on ballots, "endorsement" is not defined in statute or the measure. "Endorse" is not "nominate." The measure does use "nominate" elsewhere, so "endorse" must mean something other than "nominate."
Sec 20 of the proposed OR blanket primary says, in effect, that the political parties currently authorized to nominate by primary (ORS 248.007(7)--the major political parties) may "nominate" but does not authorize any nomination procedure, as for example, ORS 246.009 specifically does for minor political parties.
Even if by some kind of analogy or common law right of association the major political parties could decide to hold caucuses or conventions or e-vote, they could not file the ensuing "certificate of nomination" until after the primary had passed, thus they could never designate a "nominee."
When a candidate is nominated by some process other than the primary, it is the party which files the "certificate of nomination" (ORS 249.720) "not sooner than the 15th day after the date of the primary election* * *." ORS 249.722(1).
By not authorizing a nomination process for major political parties; allowing only the words "endorsed by" and not "nominated by" or "official nominee of;" and not amending the earliest date for the filing of "certificates of nomination," until after the primary; it would seem that the the major parties cannot "nominate" and no party or candidate can be identified as the "nominee" on any ballot.
If so, then the VA and MI cases become relevant.