Okay, I've seen enough of Mr. Ranma's neighborhood. I wanna write some too!
Question is, who will be fused into the Rogersverse, and who will be 
unchanged? The characters in the show (I have seen) are

Mr. Rogers (This would obviously be Ranma)
Trolley (This could be P-Chan strapped onto a board with wheels)
King Friday
Lady Aberlin (I have Kasumi in mind)
Dr. Bill (Maybe Dr. Tofu)
Anna
Mr. McFeely
Prince Tuesday
Lady Elaine (Kodachi?)
Henrieta Pussycat
Mr. Eighbor
X the Owl
Daniel the Cat

Also, should there be a lyrics change? The original is
It's a beautiful day in the neighborhood
A beautiful day for a neighbor
Would you be mine?
Could you be mine?
It's a beautiful day in the beautywood
A neighborly day for beauty
Would you be mine?
Could you be mine?
I have always wanted to have a neighbor
Just like you
I've always wanted to live in a neighborhood
With you
So let's make the most of this beautiful day
Since we're together
We might as well say
Would you be mine?
Could you be mine?
Won't you be my neighbor
Won't you please?
Won't you please?
Please won't you be
My neighbor?

I'm thinking about mashing Kirin, the Musk Dynasty, and the Mt. Phoenix tribe 
into this.

More insanefic ideas

What if Ranma finally snapped and beat the living crap outta Nabiki?
What if Kuno got hit on the head and started acting more like his dad?
What if Kasumi started malleting Dr. Tofu?