Kung-fu motif

We had two of them.

since the japanese word for 4 sounds the same as the japanese word for death, I think the 40th anniversary will have something to do with ghost hunting

Flowers or something to do with mother nature itself:)
(Like a message to children to respect the nature)

Music motif may also be interesting to see for once:D

A space motif (plantes= rangers) like kamen rider Fourze

And maybe also some American or African elements!

Another thing I want to see is card and not card-theme like JAKQ, but where the team uses cards to power up their weapons and mecha. A good example of this is Kamen Rider Blade.

Gingaman...

Kyoryuger, though having a team that actually has various music genres influencing each ranger would be pretty interesting

Flashman (sort of), but I feel like a true space motif would just make the series a rip-off of Sailor Moon and Fourze...

Battle Fever J...

And that's pretty much Goseiger...

I would actually like to see them do an all-dragon theme, in which the individual rangers would each have their own dragon mecha, with each dragon being vastly different from the others (i.e. European dragon, Chinese dragon, sea dragon, wingless dragon, etc).

Maybe a team of warrior-monks; a Sōhei, a Shaolin monk, a Crusader, a Naga Sadhu - something like that...

I'd be all over a Lovecraftian theme for some villains though....

^That sounds pretty neat. I want to see a REAL time-travel squad. Timeranger had two different years. 2000 and 3000. That was it.

A voltron/thundercats motif.

^ That was pretty much Gekiranger. The main mech and main rangers were all cat themed.

Yeah but wasn't completely a cat themed sentai.