While I'm all for original ideas, it doesn't mean that a previously used idea can't be updated and improved. Sentai has an annoying tendency to take a theme and not use it to it's fullest. While ToQger seems to be making full use of it's train theming, there's the likes of Gokaiger, that barely touched on it's pirate theme.

I'm not one to revisit an old theme just because I liked a past series that used it, but there's still a lot of unexplored potential with motifs we've already used, but for one reason or another, was spread too thin and had plenty of room to grow.

Martial arts.

Gekiranger got you covered~

But i want see another martial arts motif.

What about a paranormal one? That could be cool.

I want see a sea animal motif.

Not to mention Dairanger.

Aren't all Sentai martial arts themed? :lol

...Touche...

Actually, no. A theme is the base topic of the show, and a fight scene isn't inherently based around martial arts.