In terms of kingmaker and using the top two system to have a role, in 2016 in the US Senate race I think GOP voters really missed to boat in terms of not massively backing Sanchez over Harris. Instead, according to exit polls, 44% of self described conservatives backed Harris. Bring that number down to about 14% and we might have a new senator. (Of course would a perceived GOP Sanchez alliance have galvanized liberal support even more for Harris? Perhaps but Harris was already getting the lions share of liberal voters anyway.
Couple problems with this line of thought:
1 - Sanchez was shown to be a god awful candidate during the debates and the general campaign. Her campaign may have got more GOP voters if she was actually seen as someone who could win, rather then someone who self-sacrificed herself.
2 - Why should the GOP whip their voters to support a dem? You're not going to get one party to line up behind anothers candidate unless you spend precious resources to advertise and activate your voters. If Dems try and campaign off GOP voters, they will miss the lions share thanks to polarization. The other option that gets one party to line up behind another was seen in 2018. Feinstein was a known controversial liberal, so the GOP lined up behind the more left De Leon. Feinstein in this situation had tons of conservative scrutiny over Kavanaugh, so the ads and 'whipping' were more or less free.
And what happens if they whip their voters? Another dem goes into the senate from a blue state, takes up Shumers whip, and will win reelection in 6 years off the Dem supermajority among voters.
3 - Why should conservatives vote for a Dem? You're casting a ballot for someone who won't hold your views, and won't respect your opinions. Lets go back to 2018, which saw GOP voters motivated to simply cast a dissident vote against Feinstein. 12,464,235 people voted for Gov, compared to 11,113,364 people for senate. Over one million conservatives left the ballot blank, which would be the more rational option. Hell, the Insurance Commisioner race, with Poizner as a psudo-GOP'er got 650K more votes then the senate race - despite its position far down the ballot.
Now you might say something like this is a national senate race, perhaps the GOP supports dems locally they might foster a crossbench similar to NY's IDC. The problem with this though is that the seats that see top-two dem races are all Deep blue - the place where GOP support dooms candidates rather than lifts them up.
The problem facing the CAGOP is that there seems to be no way out of the death spiral. Poizner was the finger in the wind - a popular former incumbent against a more radical dem, in a race far enough down the ballot for ignorant Dems to drop off. There ended up being enough lockstep dem votes to put Lara in government, basically saying that the Baker route is mathematically closed here. Sure, the dems might screw up like OK/KS Rs or CT/MD Ds - but the blue moon governor is a situation that can occur in all states. On the other hand, the GOP won't die, they have a loyal but shrinking 30% base in the Far East/North/Inland South. A realignment won't save them - the modern Dem party revolves around CA so much that Clinton had to come back for cash every now and again in 2016. Its now a majority-minority state, and the GOP won't win races until they start winning minorities.