The problem with Guyver is like everyone has said... it is slow. I've being away from it pretty much a whole year, and barely a book has being covered.
Aside from that I feel 2 things have haunted Guyver when it tried to branch out:
1) Bad timing. The first 2 live action movies should have never being made -> Overall their scope was too small due to having to budget their special effects, the zoanoids too basic and they turned the series into karate super suit... so much so Sean's first exposer to us is in a dojo. The effects of the time these movies were made did not suit what ultimately we as Guyver fans would want. Ever since book 8 the Guyver story for the last few decades is based in a world Chronos controls. Ideally for a movie to be a success it has to deal with X Day and not be afraid to do it Empire Strikes back style and have the good guys get the asses kicked.
2) Don't be afraid to branch away from the manga. As everyone as pointed out, the story moves at a snails pace. One series = almost 8 books. Don't stick to the story like glue. The Live Action movies and the first OVA done something right, they tried to break away from the cast and story of the manga. If someone wants to do a detailed series they need to do the same, no content = a forgotten story. If there is some of their own originality in the story, as long as it's thought out well it gives them the ability to continue with content without having to wait for Takaya.