This seems conceptual a bit like Balan's Wonderworld, but with a lot more polish as far as I can tell. I think that concept can be fun, if done right.

It looks adorable and fun. I will probably get it around launch. I hope it's not too simple.

It looks great !
Another 5-7 million seller me thinks

The theater setting looks cool, need to see more on the game pacing 

Yeah I really like the stage play framing device as well, it reminds me pleasantly of Puppeteer, a really awesome and underrated late PS3 title.

Hopefully Showtime can showcase a similar creativity to that game.

Regarding the developer, another possibility is its being done by Grezzo or TOSE.

I think Grezzo is hard at work on Oracle of Ages/Seasons remakes and what was the last fully developed TOSE game? Aren’t they more of a support/port studio these days?

TOSE do a lot of contract work where they're not necessarily credited as co-developer but a large amount of work is done by them. I can see them taking on the grunt work in Showtime with EPD in the manager's seat.

Those the official game page specify the devs who are working on this game or does it just say Nintendo ?

Nah it only lists the publisher. (Nintendo, obvs)

Out of Nintendo's latest showcase, this was the title that interested me the most, mainly because it seemed the most unique. The theater backdrop is what makes the difference here for me.

Super Princess Peach massively disappointed me back in the day. This looks a lot more promising, and interesting. Has sparked my curiosity.