EZ-PZ, shouldn't take more than a few hours! /s

I mean, it's a basic drawing for illustrative purposes rather than a detailed map. There's more detailed images out there though.

There's a difference between removing something, closing off arteries and letting it heal; and trying to connect an organ that didn't start with the same layout. For that kind of thing, you need a bit more fine control of blood supply. Not impossible, just not as relatively easy as something like a kidney transplant where everything matches overall.

A testicle going into where an ovary normally sits is... Iffy. Slapping an ovary into the abdominal cavity would be easier to a degree, but you're gong to have to pick and choose where to connect. It's never going to be without compromise.

As it is, ovarian transplant is tricky. Tiny vessels to connect. They fail part of the time, and that's due to inadequate blood supply. Again, that's between two bodies that already had ovaries. That's still better than when they try to transplant part of the ovary, where the inadequate blood supply tends to lead to menopause in a few years. Hell, that happens sometimes when the outer layer is removed and transplanted back into the same person (it's done because of cancer or other medical treatments that damage fertility).

Allografts are not exactly magical anyway; like a kidney transplant extends life, but it's not going to last the same as your own healthy kidney would. That's exacerbated by the drug regimen necessary to prevent rejection.

Just rough guessing here, but even a fraternal twin gonad swap, where the tissue match is as good as it can get and the age of both parties is identical, you'd get maybe a few years of viable full activity. Trying to do it between people with even less of a match? Even with perfect microsurgery and blood supply, I'm doubtful you'd get a year. Maybe two.

I could be overly pessimistic in that estimate, but I'm basing it on previous successful transplants between family members.

Luckily though! Once someone manages to figure out the right set of techniques, it could extend that by years, maybe even decades. And, the drugs needed don't really mess with hormone levels, which is kinda the point in this case. Fertility isn't a factor, though those drugs don't really interfere there either.

I just don't see it happening this decade. It's only been maybe ten years or so since the first ovarian transplant between identical twins led to a successful pregnancy. Never found out if the recipient kept the ovary long term, but it does mean it could eventually be a thing. Surgical techniques take time to refine, but all it takes is one good surgeon wanting to break new ground.

Organ transplants are kind of a last ditch effort. We don't do them unless there's no other option, and for good reasons.