++Addition++John Savage responds here. He makes an interesting remark regarding the elite opinion on immigration--even if we assume the reality of human biodiversity is understood, the establishment has many reasons to lower the average IQ of the populous. Steve Sailer has summarized the elite opinion on IQ as this: It doesn't matter, but they have higher IQs than everybody else. If Steve's pithy descriptor strikes you as accurate, it's hard to argue that what John asserts doesn't describe the situation right now.
Responding to a post here on one of his own, John Savage entertains the idea of a one-drop non-white rule for preferential treatment at the national level but ultimately finds several faults in it. He points out that transnational differences, an important driving force behind whiterpeople's support for liberal immigration policies, will remain unchanged. Thus white guilt will become mocha guilt, the end result being more of the same. He also suggests that one-drop non-whites will still identify as non-whites, and thus clamor for lots of immigration from non-white places. Rather than excerpt snippets and thus obfuscate John's points, I urge you to read his post in full if the discussion interests you. My response, which I left at BNWW, is below.
The strictly national, one-drop discussion is a thought experiment. I'm not endorsing it, although I do think it would be preferable to a nominal non-white percentage requirement for preferential treatment.
No claim to a crystal ball here, either. But it's uncertain that an 80/20 white/non-white 'homogenuous' (that is, everyone is more or less mostly white with about the same amount of black/Amerindian ancestry as contemporary blacks have European ancestry--and with a one-drop rule, whites would have greater opportunity for fecundity due to greater desirability, so the mix would probably be something more like 85/15 or 90/10) will be one supportive of open immigration from Africa, Latin America, or the Caribbean. Most blacks express restrictionist views on immigration, while Hispanics tend to split or lean modestly towards restrictionism, depending on how the issue is presented to them.
Hispanics today, especially those of first generation in the US, understandably feel closer to other Hispanics entering the US than hypothetical 80%+ Euros will sometime in the future. It will similarly be more difficult for open border elites to leverage ethnic solidarity in this future, because the Indians simply won't be there (even if there is no shortage of aspiring chiefs). I suppose the pertinent question is how strongly the population buys into the tripe about one-drop. Will most people see it as a legal requirement to be exploited (in short order by virtually everyone), or as an accurate descriptor of biological reality?
Presuming only blacks and whites for a moment, were the public to overwhelmingly support unfettered immigration from Haiti or Nigeria, we'd have to throw out the working assumption that people are rationally attempting to maximize their own IQs and the IQs of their offspring. That calls into question your initial assumption that all people will have become racial realists.
Barack Obama's dominance among blacks shouldn't necessarily be taken as evidence that someone of mixed European and Other ancestry will reliably be able to appeal to Others as they rally behind him. With this presumption, it stands to reason that the mixed leader will play up his Otherness. And against an opponent who is entirely white, it will work. But against someone who is entirely Other, the mixed person will lose the battle for the Other vote.
We see this in Latin America regularly. The Amerindians back a fellow Amerindian or Mestizo who is mostly Amerindian against a more European-looking candidate (ie Morales in Bolivia, Chavez in Venezuela, Obrador in Mexico).
With Hillary as an opponent, Barack has the black vote in the bag--the mixed candidate leveraging his Other credentials to take the Other vote against the white candidate. But when he ran for Congress in 2000 against the very black Bobby Rush (who was heavily involved with the Black Panthers and is now, in addition to being a Congressman, also a preacher) in the very black 1st district of Illinois, Bobby beat Barack by a margin of more than 2-to-1--the mixed not being able to win over the Others like someone who is 'authentically' other can.