Researchers now think sperm and viruses can trade-off genes and gene-fragments. That's one of the ways viruses mutate so rapidly. Sperm interact with bacteria too, I think.
You want super-viruses? "Normalize" the charming custom of men putting sperm where it ain't supposed to be. Gay sex for the straight guy.
A woman's genital tract is an environment where that kind of permutation/combination of genetic fragments is minimized. It has the right kind of pH and mucous membranes and lymphocytes and so forth, It keeps the sperm in good shape for fertilization.
To get a bit teleological on you, I would say the penis and the vagina were made for each other --- on the cellular biology level.
Making it with a virus? Ew.