Switchblade I know that you hate Decade Kuuga and I can understand it. But as someone else who likes the original Kuuga I don't see the big problem with the Decade interpretation of it. I think it's fair to say that Rising Ultimate is the Final Form of Kuuga. But if you really need to justify that it's then just consider Decade Kuuga to be a Secondary Rider for Decade instead of an actual main series AU Rider.
Here's my personal breakdown of all of them:

-Kuuga Rising Ultimate
-Agito Shining
-Ryuki Survive
-Faiz Blaster
-Blade King
-Hibiki Armed
-Kabuto Hyper
-Den-O Super Climax (I go with this over Liner because Liner requires Ryutaro and he doesn't really become Den-O anymore. It's basically Momotaros as the rider now)
-Kiva Emperor
-Decade Complete
-W Cyclone Joker Extreme Gold (iffy on it though)
-OOO TaJaDoru or Super TaToBa (This is really a tossup seeing as the Super Medals are all more highly evolved versions of the normal TaToBa medals resulting in, obviously, Super OOO)
-Fourze Cosmic

I don't hate Decade Kuuga, per say (although lord knows he earned the fan nickname "Yuuseless"). I just hate Rising Ultimate form. Ultimate was a gorgeous suit and it's one use was an awesome moment that was the culmination of Yuusuke's journey as a character and his resolve to help others. Rising Ultimate makes no sense because the Rising powers were developed by accident and, if anything, kept Yuusuke from having to use Ultimate form. Amazing Mighty was the ultimate version of the Rising powers, and even that paled in comparison to Ultimate. Basically, the Rising powers were an unexpected but surprisingly effective way of powering up the Arcle, but Ultimate form is still the - pun unavoidable - ultimate expression of what Kuuga can be. So the idea of a "Rising Ultimate" form makes no sense to me.

And it's really damn ugly. Like Super TaToBa/Masked Form Sasword level ugly.

Also I'm a self-admitted Kuuga snob.

My mistake. I rewatched the scene and Super Climax is the form.

I understand that. That's a damn solid argument and your 100% right. I guess I've just always been a sucker for super power-ups that are absurd. So the idea of going beyond the strongest, beyond ultimate, has always intrigued me. I can't help but love things like this or other one-off forms that are absurd like Super TaToBa, Rocket States, Diend Complete, New Den-O Vega etc.

And no worries. I'm a Den-O snob :lol No way Liner Form is the final one over Super Climax. Ever.

And I acknowledged that (mostly. It's unused, not non-existent). However, it was designed to be Double's alternate form. If we're onky talking about forms that extend beyond the blueprint, then yes, I would say CycloneJokerGoldXtreme would be Double's final form. Otherwise, I'm just going to go with Shroud's word. But if you want to disagree, go ahead. Your reasoning is understandable (in my opinion). And since we're on the topic of snobs, I'm a Double snob.

I'm sorry, but without seeing CAX in action, there's no real way of gauging just how powerful the form really is.

Word of Shroud. Shroud created the tech for Double and Accel, so she should be able to figure out Double's most powerful form. She said it was CAX, so I'm taking her word for it. CJGX only really has wings and a new color-scheme.

You can't really gauge a rider just based on word of mouth...Cosmic States is suppose to be Fourze's most powerful form, yet it still got it's ass handed to him by Leo Zodiarts.

Another example:

They kept going on about how powerful the Zangyaku were in Gokaiger, but they never did a damned thing to show for it.

Just cause they say something is ZOMG TEH STRONGEST EVAR! doesn't nessicarily mean it is...for all we know, Terui and Phillip could've been totally incompatible with one another, thus rendering Shroud's word useless.

They never even attempted to bring CAX Into play, so there's really no point in debating about this.

Who's to say Leo isn't more powerful than Cosmic States? Besides, CAX is technically more powerful, but only in the the sense that attacks like those of the Terror Dopant would be ineffective on CAX, as the users would be immune. W established that quite nicely. I see where you are going, but I think I'll trust Shroud's judgement.

I never watched Gokaiger…

And actually, they did attempt to bring CAX into play, after Shotarou was unable to be Double. Besides, Philip has all of the knowledge of Earth in his head (more or less). He'd probably find a way :).