[Red5]

I had this idea a little while ago of them doing a youkai (ghost) theme since it will be the 40th and 4 in Japanese sounds like the word for death. I know I say this idea a ton, but it would be a cool idea. They could exclusively enlist the help of the sentai rangers that have died in the past (or just their suits and powers) as the story progresses. I think five have died and not been replaced (Black Condor, DragonRanger, AbareKiller, Time Fire, and Beet Buster) and that is where the main five rangers can get their power ups from. Instead of the team all getting them at one time, they could each help satisfy each ghost's final wish or something and be rewarded with a power up. And if Akira (ToQ6) dies like he plans, it could be a power up for the sixth ranger. It could be an entire season based on ghost hunting or helping good ghost rest in peace.

TLDR - Sentai Ghostbusters.