What do you think about a skillsoft granting ambidexterity? A cyber arm with the muscle memory of a dominant hand?
I not trying to game the system, just thinking out loud and coming up with explanations for characters that buy ambidexterity after character creation. (Other than "just practice")
I don't see the skillsoft being viable. Activesofts literally replace your control of your muscles and uses preprogrammed memory. That means you don't have ambidexterity or even dominance in either hand, as you aren't controlling your body. As for the cyberarm, I don't see it there either. Ambidexterity is a brain thing, not a limb thing. Magic can give ambidexterity, so I would say you could have headware giving ambidexterity, but I doubt it would be invented. Ambidexterity doesn't really provide you with a substantial bonus (not in game terms, in real life terms), so I can't imagine that a corp would spend 100,000+ nuyen in research and development to create an implant that probably costs 10,000+ nuyen just to give someone ambidexterity.
So, you could create stuff as a houserule, but under the current rules, I don't see it happening. As for characters that buy it after creation, that's them mentally exercising themselves to become proficient with both sides of their brain, which leads to them being dominant in both sides of their body. It's a flavor thing, and a mechanical thing if that specific character really wants ambidexterity. Shoot a gun using your off-hand enough times, you start getting a little more effective with your left hand. It should be noted that even ambidextrous people cannot do everything with both hands. I have a cousin who throws football with his left hand, but writes with his right hand. He cannot write with his left hand, but he's still what you would consider ambidextrous.