People are going to extradite me, but I actually want Power Rider to be a direct sequel to Masked Rider, revolving around Dex's son, Lex, who must travel through the History of Edenoi to gain the powers of the First Masked Riders. And Decade would make sense to adapt that.
No because Decade is only 31 episodes short with only a couple of movies. And since Toku adaptations are usually a lot shorter than the source material, that would make it a 20-25 episode series (unless they're willing to spend extra money on American footage, which is too risky for a franchise that hasn't proven to be successful in America).
Splicing footage with the other 9 Rider shows would make it extremely awkward and only the fans would get why the other Riders are there. The general audience will be like, "Who are these people and why should we are about them?"
Can't recycle footage over and over again either. Because it worked SO well with Masked Rider.[/sarcasm]
On top of all that, they're introducing Kamen Rider to a new audience since Masked Rider was an old 90's show that nobody remembers and Dragon Knight suffered piss poor ratings. Do you honestly believe a
pink or
magenta male superhero is a great way to start?