ZX was around for a good four years or so before that TV special right? (do you know if that rumor about Ishinomori and Hirayama being unable to find funding for a series is true?) I always thought it would have been kinda cool if they tried pumping out new Riders like that during the big 90s break.
I don't know the exact details, but fans wanted another Rider. Ishinomori did create another, but something happened and he decided to go for a different type of media than TV. ZX was on a radio show before it got the TV special. I really don't think it had something to with the funding.
I've always heard some crazy stories about what series were originally going to be called and the stuff is really cool to read about. I think I recall once reading that Black was going to be called Kamen Rider 0 / Zero at one point to signify a complete cut off from the previous shows and try to adapt a version of Ishinomori's original idea for the first show.
You're right, Black was called 0. I believe it was supposed to be a new origin story to the Kamen Riders or something, which is why he was called 0. Not sure why they changed it to Black though.
The picture below is an early sketch which mentions the name Kamen Rider 0.
I have read that RX actually stands for "ロサ・キネンシス" which is the flower, rosa chinensis. Although, I don't see how RX is connected to that flower.
I'm just going to throw out whatever I've heard/read. Not sure if all of it's true though.
Kamen Rider Agito: Agito means "I move", which was supposed to represent how Agito kept evolving. The omega at the end had some meaning, but I forgot what it was. I think it had something to do with "the end". Agito is also an obsolete word for chin.
http://dic.yahoo.co.jp/dsearch/0/0ss/100175500000/
Kamen Rider Gills: The very same kanji for agito/chin could also be for the word gills. Gills was more or less an incomplete Agito.
Kamen Rider Ryuki: 龍騎 as it's written in Japanese. 龍 (ryu) means dragon, 騎 means roughly to mount. The guy does ride a dragon bike.
Kamen Rider Hibiki: 響(Hibiki)- echo/sound 鬼(ki)- demon/ogre. Sound is a key element and the guy is supposed to be an ogre.
Kamen Rider Kabuto: Kabuto is based on the kabuto beetle. I do remember that his early name was 甲斗, which is pronounced Kabuto as well. 甲(Kabuto)-Helmet 斗(to)- it's a type of measurement. Not sure how it was incorporated in the actual series.
His final name in Japanase was カブト, so it was slightly different.
Kamen Rider Sasword: From the word sasori, which means scorpion, and the word sword.
Kamen Rider Gatack: From kuwagata, the type of beetle he was based on, and attack.
Kamen Rider Den-O: Train King. He's based on trains.
Kamen Rider Zeronos: From the word zero and Chronos, which was supposed to show that everyone would eventually forget about him. Chronos was some sort of time god or something.
Kamen Rider Kiva: King of Vampires, pun on the word kiba which means fang.
Kamen Rider IXA: Read the same as the word 戦 (war, fight)
Kamen Rider G: Because he is the true O
G