i believe thhey meant the Megaship from MegaRanger.

I think the space theme is not popular like before.

It could work. Especially with the renewed interest of the space sheriffs, thanks to the recent movies and crossovers.

Would be cool but I understand the concept of protecting the earth serving as a mainstay for the series.

We could have another mechas like of the megarangers ?

Like Megaranger how? If you mean a spaceship, I guess so.
If you mean in reference to it being a 1 piece mecha, 6th rangers tend to get those on a yearly basis.

What about flashman?

Space themes is not popular like before.

It wasn't set in space. The Rangers were from space (kinda) but it mostly took place on Earth.

An interesting show to check out might be Juspion. The first few episodes are entirely set in space and show the character planet hopping looking for an item before it settles on Earth.

The biggest issue with doing a show out in space is definitely the question of cost. The reason Sentai always takes place in modern day Japan is because it's the easiest, cheapest setting to film. Anything else and you have to start building sets and probably get extras into costume. This is one of the drawbacks of tokusatsu compared to anime.

What they could realistically do, though, is set a series in feudal Japan. Toei produces quite a few period dramas and so they always have period costumes and sets at the ready.

Damn straight they do. Abaranger, Dekaranger, Shinkenger, and a bunch of different movies had extended sequences in those sets. Probably way more than those which I haven't seen yet. Toei even had Kamen Rider OOO cross over with one of their period drama stars for its time travel movie.

Because they probably don't have a big enough budget to design different alien races.