This isn't really an outright accusation, but has someone thought on the basis that Red John, is a woman, one who we have met only once before, just on a simple, usual case. One who Jane has met only once before.

One person so smart that she managed to fool everyone into thinking that they were a male? It would be the perfect disguise.

For all of the tape recordings, Red John could use an accomplice's voice, or if he's as talented as Jane(which he clearly is)could hypnotise people into recording them for him.

When Red John was accused of rape-ing Lorelei's Sister, do you think that he/she would have been smart enough to not actually rape her? I mean, they could do a DNA analysis on the sperm and find out his identity!

OR

It could be a man, posing as a woman posing as a man...

Honestly, I have no idea. But y'know, everything is possible...Right?

AND doesn't Red Johns symbol seem very similar to the Death Eater's symbol in Harry Potter?

Physically, they look different, but both are described similarly:

Death Eater Symbol: "Just picture coming home and finding the Dark Mark hovering over your house, and knowing what you’re about to find inside."

Red John's mark is described as very similar(except for the fact that it doesn't hover... "You see the mark first, and then you know what's happened."

I'm sorry, I couldn't resist.

So, overall:

. Red John could be anyone
. We have no more of an idea of who he is than the CBI do(unless it's one of them O.o)
. Red John likes Harry Potter? 
. Nobody has any idea who Red John is. In fact the only thing we have is "You've shaken hands with him before"

Aha! Now, who else is going to go back, watch all the episodes from Season 1 and list all of the people Jane has shaken hands with ever.

Just me then ... Ah well.