If (masses of) women really had a need like that, they'd buy the current tech magazines - it wouldn't fit the niche perfectly, but it would at least partly fulfill that need.
They don't. Which is evidence that there is no such unfilled niche.
Or, much more likely, they aren't interested in the male focus of said tech magazines. See https://news.ycombinator.com/item?id=6738657 for a quick look at the covers of the tech magazine T3. Are you saying the average woman would really want to read a tech magazine with that sort of focus?
We're not talking CACM here; we're talking tech magazines that, for the longest time, celebrated conference booth babes.
If what you say is true, then all the world's women with the desire for reading tech would flock to the few tech magazines that have less of "that sort of focus", they exist. This would cause these "non-booth-babed" magazines to have a disproportionally large amount of women buyers, which they would see immediately... but it's not happening.
Reality is that which doesn't go away if you disbelieve or dislike it.
Reality being that which doesn't go away if you dislike it, I recommend you look carefully at those supposed tech magazines with “less” of the young male focus that you claim exist. You'll find that they don't, really, outside of quasi-academic magazines like CACM. Even there, it's hard. How many women are on staff? How many of the articles are written by women? How much do the articles focus on metrics, measurements, and numbers as opposed to usability? I really like reading AnandTech, but as a tech magazine that isn't interested in booth babes, it is still deeply focussed on the male interest and experience with tech, as the masthead (http://www.anandtech.com/home/about) with it's conspicuous lack of women on staff indicates.
Reality being that which doesn't go away if you dislike it, the reality is that there are no mainstream tech/gear magazines—online or print—that don't use a hypothetical young male as the primary audience for that magazine, doing a disservice to both those young men and the young women who might be interested but aren't interested in the editorial slant involved.
Reality being that which doesn't go away if you dislike it, you're a guy—as am I—and we don't actually get to say that something we like is not sexist in its nature. There are things that I will read that I know are sexist (and not care that they are because I want to read them anyway), but I don't get to pretend that they aren't sexist just because I like them.
As I said above, "it wouldn't fit the niche perfectly, but it would at least partly fulfill that need".
If they aren't buying the currently best-fitting magazines (even though they just partially fit the need), then they are showing with their wallets that they don't really want it; and the magazines are completely right to do as they do now instead of throwing resources to serve a nonexistent/tiny market.
If all the women buyers would go to the magazine which currently has the least "male slant", then they'd be 90% of the audience for that magazine, which the publisher would immediately see and they'd get attention.
If noone prints anything even remotely acceptable but the readers would really want it - then they'd get that need filled on online media. Is there a booming audience of women tech bloggers writing for women readers and getting huge audiences + ad income that would justify targeting a magazine directly at that?
There will be articles written by women for women only if they actually put their money where their mouth is - if someone (+ millions like them) are not going to buy the resulting magazine, then saying "there should be a mag like that" is empty talk. Even if it's unfair and sexist, if the buyers aren't there then such magazines don't have a reason to exist - that's reality.
There are just no women reading it. So you might consider the possibility, that maybe - just maybe, women are just not into this stuff. And that women publishers are savvy enough to know what their readers want covered.
They don't. Which is evidence that there is no such unfilled niche.