remaining human genome variation that hasn't been sequenced? Given all the genome variation information we have accumulated from resequencing human genomes up until now (early 2018), how much variation is left that hasn't been sequenced?

EDIT: given one of the answers, and the fact that 99% of the SNPs at 1% or more are found, is there a quantitative measure of remaining variation?
In theory, almost any base in the human genome may mutate, so you have billions of variants to go. Ok, this is not so useful.

A related and potentially useful question is: given a human, what is the fraction of his/her variants seen in the the previously sequenced samples? For a Wright-Fisher population, there is an analytical answer: x% of variants on a haplotype has frequency below x%. Replace "x" with "1": 1% of variants on a haplotype have frequency below 1%. The 1000 genomes project concluded that 99% of SNPs at frequency 1% or higher have been called by the project. If we all came from a Wright-Fisher population, 99% of of SNPs have been called in 1000g. Given that the project also calls SNPs at lower frequency, nearly all SNPs in a newly sequenced sample are present in 1000g.

The above is a theoretical analysis. In practice, there are two major complications. First, we are not a Wright-Fisher population. Due to recent population expansion, each haplotype harbors more new mutations than the Wright-Fisher model would predict. Given a known population history, it is actually possible to numerically compute $f(x)$, the fraction of variants with frequency below x (for Wright-Fisher, $f(x)=x$). I don't have this result, though. Second, 1000g and many other genome projects didn't call SNPs in repetitive regions and missed a significant portion of high-frequency indels and structural variations. With Illumina, you can only call ~30% of long deletions callable with PacBio data, but we only have a dozen of PacBio human genomes in public. There are still a lot we don't know.