Testosterone levels vary wildly from person to person based on different conditions, but if you look around you can find reference ranges for men and women. The reference ranges for "Average" male and female adults from one source are:

  Avg. Adult Male   270 - 1,070 ng/dL
  Avg. Adult Female  15 -    70 ng/dL

So the top end for women is much smaller than for men, but it's not actually that far from the lower end of the male range. These are "normal" ranges, and some (otherwise) perfectly healthy men are below the bottom end, and some women are above the top end.

One might expect that ovaries don't produce testosterone, but in a typical healthy XX woman the testosterone in her bloodstream is produced by multiple parts of the body. So while an XX individual has low levels, there are multiple sources of it in their physical makeup, and it's at least theoretically possible you could increase production.

As far as estrogen goes there are some easy ways to produce it for an XY individual but the side effects are pretty severe :) Some otherwise healthy XY men have various genetic or other maladies that cause their body to produce unusually high levels of estrogen by itself, so assuming you could control for the undesirable side effects, it's clearly possible to do that too.

Personally, I don't think we're going to get a good handle on producing the hormones necessary for MtF and FtM trans people in the body naturally anytime soon, but it seems feasible to me. And it would certainly be helpful to cis people with unpleasant hormonal disorders.