[Tokumonkey]

I like your reasoning, but I still think that it's extremely unlikely that Toei will choose a female main Rider. The sticking point is marketing: modern Kamen Rider is all about toy sales to their target market of young boys. A big part of the sales figures (if I understand correctly) is roleplay items, and I can easily see Toei being skittish about young boys turning up their noses at roleplay items "for girls."

If they were to go with a female main Rider, I assume it would be Bandai experimenting with marketing to young girls. It's not entirely outside the realm of possibility that they might try this, but I doubt they'd dive directly in. I suspect they'd want to test the waters by debuting a series with two main Riders, probably brother and sister, most likely sharing the same weapons/items, so as to as to avoid the "cooties" problem. (And to be clear, I'm not talking about what kids actually want or would respond to; I'm talking about what media/toy companies think kids want.)

I would love, of course, to be wrong. I don't like that female Riders have been so rare, and usually been relegated to tertiary status. Seeing Toei/Bandai take a chance would be really exciting.