So lately in terms of story telling I have found DCU to be superior to that of marvel so this would just be my own personal idea. It's crazy and probably make no sense but it won't leave me alone! >_<
So this is what I have, Ranma is actually a kryptonian, when Superman or Clark Kent was 18, another meteor shower hit the Earth again , Johnathan and Martha kent remark how it is so similar that brought clark to them. Over in Japan, Nodoka was stressing not being able give Genma a child when the ship of a small carrying Ranma crash on her lands. Genma return a year later from a training trip with Happosai to find he now has a son and assume it is his.
Now as for the whole strength part, I would suggest using the idea that as a child a Kryptonian is weaker and eventually get stronger as they age. Since Martial artist are power in their own right the baby shouldnt cause too much of a rucks. I think the neko ken incident will stunt Ranma power growth a bit, might have a bit of a mix match that show all the cat in the pit was burned via Ranma X-ray vision and Genma couldn't be more proud.
Now here's the kicker, he is not related tot he house El- In stead he would be of a different house, not a genius mind you but someone who believed Jor-el about the planet blowing up and had a small ship built for his son also.
We could also have it where because Ranma is training constantly he is expending the solar power he normally absorb on a daily basis there by not building up a reserve at all. Since he sleeps at night he not taking in any solar power and Genma getting him up at the crack of dawn ensure his solar energy continue to be expended. Once he get afflicted with the Jusenkyo curse that effectively put more of a dampening on his power since his girl side is human and thus not absorbing powers.
Well back to the potential story. I think the whole fiancee thing should play out,with him expending his powers to fight all the time he is not building up a true kryptonian charge. Also , We could have Akane buying a jewelry necklace that make's Ranma weak and this malletable, but since it a tiny piece doesn't have the visible effect of making Ranma sick like it would Superman. And because Cologne could be said to use magic along with all the magical stuff Ranma deals with he get hurts enough that no one thing he's a kryptonian, after all Superman is weak to magic.
So Herb and Saffron fight could have killed him. However I think having the big revealed would be during the Saffron match when he had to use more powers then he had and because he was rested enough over the two years mostly he build a big enough reserve that flare him out to Superman Computers indicating another Kryptonian.
Of course at this point in time in the DCU, this would be when Supergirl first returned and before the whole Crisis battle. The way I see this end up is a match up with Supergirl.
Many things can happen depending if you want Ranma to participate in DCU storyline arc or just want him to do a meet and greet with the cast of the DCU. But that's how I see it.
Whew.