To begin with, an assumption
We live in a more politically diverse world than we once did. You say "mixed-gender" but follow with a discussion about men and women. That's not necessarily a bad thing, because the pros and cons of the world's current views about gender are remarkably complex. IMO, too complex to handle in a single question.
So, cheers for working with one, specific condition.
There are many reasons why women have been a challenge in the military
In my opinion, nobody in their right mind would dispute the value of women in the military. Likewise, nobody should be arguing over whether or not women should have the right to fight for the people and the nation they love. But that hasn't shortened a very long women-shouldn't-be-in-combat attitude.
It was a surprise to read an article about women finally getting flak jackets that fit. Surprise, surprise! Women are shaped differently than men! And when did we finally solve this problem? June, 2021... and that only after an Act of Congress forced it to happen.
But it underscores the problem and frames the nature of your answer.
It's not just about strength
It has been long established that, when comparing male and female atheletes at peak performance, men outperform women. From a technological standpoint, that means you need a way to...
- Improve strength
- Improve agility
- Improve speed
SciFi has often used the idea of an exoskeleton. Powered armor has been the favorite, but I've often wondered how you'd fit a human inside powered armor. The powered exoskeletons shown in Edge of Tomorrow (2014) are, IMO, more realistic.
There are other physiological differences including, in men, thicker skulls, longer limbs, etc. However, that exoskeleton combined with good head armor solves all that.
As mentioned earlier about flak jackets that fit, there's the simple reality that, generally speaking, women are shaped differently than men. But, technologically, that's fairly simple to overcome, too. The U.S. military could have done it decades ago. They just didn't think it was important due to, frankly, millennia of belief that women shouldn't be in combat.
But there are some biological problems
Things get a bit more complex, especially logistically, when a military must start considering the requirements of mensturation and child bearing.
Let's start with child bearing, because I don't believe it not just a technological issue when it comes to keeping women active in the military. Yes, through chemicals it's possible to keep women from childbearing, and it's reasonable that a woman can choose to avoid childbirth indefinitely to devote themselves to a military career. What isn't reasonable is to assume or compel that choice.
And here's where technology isn't sufficient. Should a woman choose to conceive, then the military's only real choice is to relegate the woman more and more to non-combat duties until imminent childbirth and early child rearing demands her full attention for the success and health of both mother and child.
This is only one opinion about how childbearing and the military might collide. Others may have other insights. I don't profess to know definitively if what I just suggested is the best perspective.
Menstation is the next issue, but today, chemistry can overcome that, too. Great advancements are being made to allow women to serve fully and to their utmost capacity in the military.
It appears that humanity has already solved two of the three problems:
With chemistry, we can manage menstration and childbearing, leaving the later as a choice, not a problem to be suffered by either soldier or the military.
And only conscious regard was necessary to overcome the problem of properly clothing and outfitting both male and female soldiers.
From this perspective, 2023 technology is sufficient. The problem is making personal, physical strength, agility, and speed irrelevant.
- The use of a powered exoskeleton to make all soldiers equal.
Humanity is working on powered exoskeletons for combat and is testing existing solutions for powered prosthetics. At the rate of current technological advancement, I'd guess that the first practical combat exoskeletons will exist in the next 20 years.
So, what's your answer?
I predict that human technology at 2040-2045 will be sufficient to wholly equalize the sexes during combat. Or, perhaps it's better said that gender will become irrelevant.
I've treated combat soldiers as if they all do the same thing in the same way. That simply isn't true. There are specialized combat forces, combat engineers, combat medics.... There are combat specialties that are gender-irrelevant today and have been for a long time. I'm answering in the most general way possible.