Blue as 2nd in command isn't really a thing, you know. Black/Green is more often the one to take that spot.

Aquaman is pretty damn badass, so I think a Merman could work just fine as a second in command.

Aircraft, or any other form of aviation!

I'd love to see another ninja themed sentai, personally.

I'd say Ninja and Space, but if they did do a space theme after Toqger, or after the season that follows that up, people might think it's a rip off of Fourze.

Dragon rangers...

Didn't Fourze not do so well?

Didn't we already have an aviary-themed Sentai in Jetman?

Yes, but was there a triplane mecha? I think not! :p

But that was 20 years ago...

I think what he may be implying, is perhaps using old ideas isn't for the best right now, as we still have so many untapped original ones.