I'm with ya, Bill, but a few observations and comments.
The original question here addressed wording about WikiTree DNA "confirmation" and the X-chromosome that was removed the latter part of 2018. That said, however, there are some that want it brought back. I'll address the male vs. female thing in a sec.
First, though, we need to recognize that there are powerful reasons that none of the DNA testing companies perform matching based only on the X-chromosome. None; ninguno; aucun; keiner. In fact, only 23andMe even includes the X amount when reporting the total DNA shared with a match. All the other companies stick to reporting information only about the 22 autosomes.
In a nutshell, the X-chromosome, while undergoing recombination at frequencies not radically different than an autosome of the same size, still proves to be markedly more volatile when it comes to using it to estimate relationships. For some examples, genetic genealogist Jim Owston wrote about it here; Jared Smith here; and Roberta Estes here. Not only can xDNA segments be "sticky" and date back many generations before a hypothesized MRCA, but in relationships as close as grandparent/grandchild it's possible to see the X inherited 100%...or zero. By itself, it's a wholly unreliable predictor of relationship degree, and a shared xDNA segment--even one that is triangulated--may be meaningless as accurate evidence of the MCRA unless combined with additional autosomal evidence.
There is only one thing special about the X-chromosome in relation to males: as you note, Bill, that's the inheritance pattern. The important distinction for genealogy is that, in males, the X is "naturally phased"; it was Debbie Kennett a year or so ago who reminded me of the term. ISOGG succinctly defines phasing as "the task or process of assigning alleles...to the paternal and maternal chromosomes." Every male's X-chromosome comes from only one place: his mother. Ergo, it's "naturally phased."
However, there have been continued misconceptions that that condition also infers upon any xDNA sharing between male cousins some additional super powers: that even tiny segments can be relationship predictive, and that triangulation is unnecessary...where, conversely, between two females, or male and female test-takers larger segments are required and that triangulation beyond 3rd cousins is needed. There is no scientific justification or existing experiential evidence for this male-matching favoritism.
At oogenesis, the X-chromosome undergoes crossover--recombination--just like any autosome. Blaine Bettinger began the "X-DNA Inheritance Project" two years ago. I don't believe it got anywhere near the traction that the Shared cM Project did, but Blaine's interest was in compiling information about xDNA recombination. To do so, he used GEDmatch to analyze grandparent/grandchild only: a necessary step back from the parents, but not so far that the crossover events couldn't accurately be analyzed. After 150 unique data submissions to the project, he charted the per-meiosis event X-chromosome crossovers against those of Chromosome 7 (Chr 7 was chosen because it is relatively equal in size to the X: 159 million bp vs. 153 million):
What he found was that--regardless of whether the test taker was male or female--the inherited X went through recombination in a frequency not disproportionate to an equivalently-sized autosome. The X-chromosome had a slightly higher chance, 3.3%, of seeing no crossover during a given meiosis event, and a lower probability of a greater number of crossovers per event. The greatest probability was two crossover events per birth.
With the exception of the X-chromosome's two pseudoautosomal regions, which aren't evaluated for genetic genealogy anyway, the X goes through crossover in the mother, not the father. If we step back to the 2g-grandparental level--3rd cousins--the male test-takers' X-chromosome will have gone through crossover either three or four times before he inherits it; at the same relationship level two female test-takers' X will have gone through crossover either four or five times.
So for two males, the complete circuit from 3rd cousin to 3rd cousin could see a maximum of eight meiosis instances of crossover. For two females, the same complete circuit could see a minimum of eight meiosis instances of crossover. There is no difference in the potential xDNA recombination between those two scenarios.
Other than the naturally-phased condition of the X-chromosome in males, absolutely no conclusions can be drawn regarding evidence of relationship, size of relevant chromosomal segment, or removal of requirement from triangulation when two males are compared vs. a male and female or two females. I personally would never use xDNA in a vacuum as evidence of any genealogical relationship. It's invaluable to use in conjunction with autosomal data in order to isolate an inheritance pattern, but an X-chromosome match--even a relatively large segment--really doesn't mean much by itself.
