And that's putting it mildly. But to be fair it didn't tank because of the story. That was part of it, certainly. But mostly Go-Busters failed because it didn't have a gimmick. Goseiger had cards, Gokaiger had keys, Kyoryuger had Batteries, even ToQger had trains. Go-Busters didn't have any of that.

I think the spy theme could work again. Just need a gimmick.

They should have had the buddyroids be these sentient usb sticks that became their henshin item.

The story was also a problem, but more thanks to the timing. Only one year after the disaster that was the Tohoku Earthquake, the children also had major problems with the show because of how real it felt. Think about it: If you (as a child) had lost your parents only one year before, you also would have problems enjoying a show where the heroes deal with the loss of their parents.
It's the same with Ohranger and the Tokyo subway sarin attack, but Ohranger luckily had better toy sales.

I believe that at that point, Japanese children were still to traumatized to deal with the seriousness of Go-Busters (also with the fight around an alternative energy, which was also very real at that time).
And I think that's why Toei postponed military themes for a while- same with Ohranger, which was followed by Vehicles (Carranger), Video Games/Electronics (Megaranger) and classic Fantasy (Gingaman)- GoGo V took a step back towards the more "serious topics" with the rescue theme, but I think the real "serious" stuff didn't start again until Timeranger (anyone who has seen GoGo V might correct me here).
And considering how much of a disaster Go-Busters was, compared to even Ohranger... I guess it might take even longer this time.

I think GoBusters' theme could work again. It's just the tone that won't be brought back with it.
I think a military or spy theme isn't a death sentence for a series, it's just they try to play them straight and too seriously, which is the problem. Disasters happen all the time, it's not just due to ironic timing. A serious military Sentai will always hit too close to home.

Well, even with a light-hearted spy-theme... it is yet too early to re-use it anyway. It usually takes some more years before a theme is re-used for a new season and Go-Busters isn't that old yet.

According to dukemon22 from Toku Insider:
Some rumors have come in for the 2016 40th anniversary sentai and the theme will be:
"Murmurings on the Japanese boards have pointed to next year's motif being "Space + Insects" (Uchuu + Muchuu)"

Eh, why not.
We already gave the riders four wheels instead of the standard two.
I am game for anything at this point.

So for the 40th Anniversary they merge Kamen Rider and Space Sheriff into a Sentai. I'm totally down for that.

Space and insects? Fourze redux?

Anyway both space and insects together sounds like the PERFECT theme. :D

Rumors are more than likely fake at this early.

However, we SHOULD have a name trademark by about this time next month.