A modern jetman with mechas like the timejets would be awesome.

No no no. You said something else, which is why you were corrected.

You specifically said mecha. Not themes, not designs, but mecha, in which Changeman was just another set of military vehicles.

I mentioned a Egyptian theme on my facebook once. I had a similar concept on the mecha however I said that each mech switched out the torso to make a robot equivalent of the god they represent. I to had Set as the bad guy but as a six ranger that is bad but turns good. But that's overdone. Anyway I also said that King Pyramider should be brought back and also include a sarcophagus that summons previous robots and mecha to aid the new team. Also I stated that the helmets should have hieroglyphics as the visors.

If an Egyptian concept, give it a Yu-Gi-Oh! vibe!

Insects. Japan loves their bugs!

Huh. I guess I mis-remembered that. My bad.

It's cool~

I imagine this would clash too much with Kamen Rider. Even when the Riders aren't based on insects, it seems like that's too sacred of a motif for Sentai to use for its main team.

We probably won't see anything military or tech heavy for a while, that stuff doesn't do great with Japanese kids in the last couple of years. Personally, I would love it if Sentai tried out a musical motif. Kyoryuger sort of came close but music was more of a theme there than a motif of the suits and toys. I'd like to see a full on musical Sentai.

Granted, the only problem here is that both times Toei and Bandai have tried musical motifs before (Kamen Rider Hibiki and Suite PreCure) the shows really under performed. Maybe third time's the charm?

What about a monster theme since Kiva?

And if they do another animal theme, how about something like OOO?

Red - birds (hawk/eagle, peacock, condor)
Yellow - felines (lion/liger, tiger/panther, cheetah)
Green - strong animals (rhino, bear/gorilla, elephant)
Blue - aquatic creatures (shark/orca, eel, dolphin/octopus)
Pink - canines (wolf, fox, coyote)

Extra rangers:
.....

Evil rangers:
- Violet - extinct beasts (sabertoothed tiger, mammoth, doedicurus)
- arachnids (spider/black widow, scorpion)

They're doing an animal theme right now though. They aren't going to instantly follow it up with another.