If I am not mistaken, Don Momotaro's next upgrade Form is using a Vermilion Bird power in one of the newest rumour. Since Don Robotaro's chest armour in DX version is can be removed, I think Vermilion Bird-themed Robotaro can become a chest armour and can combine with Don Momotaro and Don Onitaijin.

Maybe the final Robotaro is Black Tortoise. Maybe this Robotaro is typical huge final robot.

Why is Don Dragoku Alter green instead of gold? After all, Don Dragoku IS a gold ranger. And why doesn't Don Torabolt have an Alter?

Honestly Don Dragoku looks more like an orange ranger with gold armor to me, but back to your question:

We have no idea, but the Dx Avataro Gear set 5 comes with the Dragon Ranger and Don Dragoku Alter Gears, so maybe there's a connection?

So Don Murasame will be the one to use Hurricaneger powers

If you notice the trim color of the two forms Don Dragoku is clearly a nod to Ryuseioh(which is also inspired by Sun Wukong) and Don Torabolt is Won Tiger. And The dragon and tiger together are a very popular dichotomy in Asia. As for his Alter form the color scheme and motif is likely a nod to Dragon Ranger.

It’s a shoutout to Dragonranger, the first 6th. They’re trying to reference as many 6th warriors as possible.

I just love how right off the bat they give us nods to Zyuranger, Dairanger, and LuPat. :lolol

Some new HQ images of Don Doragoku.

Some funfacts from this weeks Donbros blog
https://www.toei.co.jp/tv/donbrother...9221_3246.html
Apparently one of the original ideas for Donbrothers was for it to be Journey to the West themed instead of Momotaro themed. This idea got shelved cause of confusion on how to incorporate the theming, and because Dairanger and Kakuranger already has some Journey to the West theming.
The idea to make Doragoku dragon themed was to separate him from SaruBrother who was already monkey themed, citing how Ryusei-Oh from Dairanger was a dragon with Son Goku influnces, so Doragoku is kind of the reverse.