@ TrEs-2b that is wrong. Random but increased Mutations Happening to a Fetus cause malformations and very exotic tumours, so the individual might not even survive and yet not have particularly Special germ line cells.
If the Virus by some mechanism was present/active mostly in the ovaries and/or testes, sure why would that not work?
Infected People would likely have a lot more stillbirths than is normal, and then some Kids who are extraordinarily different in ways that may or may not be an evolutionary Advantage.
However if an individual born to infected-in-adulthood-parents, who has some traits that sort of make them the first step in a new evolutinary path, can never stabilize/multiply that line if their own attempts at reproduction were to also involve increased mutations, because they would lose many offspring to letal mutations and then have some where grandparental Status was reestablished, and also some Kids who share most of their new traits plus each have a bunch of newer ones of their own.
Seeing how genes interact in complicated ways and how many mutations are recessive and only have effects in the homozygous state, that would be way too much variation, and likely lead to many promising lines ending after one generation…
To accelerate Evolution, I recommend a Virus that does not pass from mother to child and is generally not particularly contagious, so only a few individuals in each generation will be affected and have a lot of mutant children, and the ones among those whose mutations make them advantaged reproduce more than average, and then someone with some new-ish traits, whose great-grandmother was a virus carrier, gets infected again and produces offspring with many new mutations, and that is still accelerated evolution… Invent a vector for this virus that would make it plausible to only surface once in 100 years or so.