I sure as hell would. I took enough time to write a blog post about it ffs.
http://plebegaming.wordpress.com/2014/07/04/would-mario-fit-in-an-open-world-yes/
The gist of my complaint is, why hasn't this already happened? We had Mario 64 which was close to a 3D adventure platformer game, but we've regressed back to more linear game play. I love Super Mario 3D World even more than Mario Galaxy, but I still wish it had more open ended stages with multiple goals.
Something I really miss from Mario 64 is the flying. Yes you can fly in Galaxy but it's nowhere near the same. Could you imagine donning the cape again, I prefer the cape to the look of the flying cap, and flying across the entirety of the Mushroom Kingdom(s)?
To me it feels like the open world games of today focus heavily on violence and "gritty realism," but I would much rather have an open world setting let me explore the lands I've seen since I was a child. No guns needed, just let me run, jump, fly, and occassionally stomp on goombas.
EDIT:
Mario 64 is the perfect example of what an open world Mario game could be. Simply remove the hub and add worlds from SMW and SMB3 reimagined in 3D and situated seamlessly into one sprawling world. The design of the world is already somewhat planned out thanks to previous overworlds, simply arrange them all in nice positions relative to each other.
In Mario 64 you were able to attack platforming in several different manners, and it certainly didn't hurt the game in the least considering how consistently it's ranked the greatest of all time. To get a bit of what I'm imagining:
Imagine you're in an HD, upgraded version of Bob-omb Battlefield, now you climb to the top and you see the changes that were made. Instead of a boxed off area, the battlefield is now surrounded by rolling hills. Depending on which direction you look you see familiar areas. To the North you see a mountain range, with one mountain in particular above them all: Tall,Tall Mountain. To the South the hills give way to the Donut Plains. If scale Tall, Tall Mountain you could procede onwards to Snowman's Land or you could use a cannon that you find on the summit. With a well aimed shot, Mario can reach a suspicious pole dangling from a cloud that's passing by. Shimmying up this pole reveals Sky Land. Alternatively, if Mario visits the Donut Plains he could opt to tackle one of Bowser's strongholds or dive into the lake. Inside the lake you could find a hidden underwater path into the Vanilla Dome, which houses the Dire Dire Docks.
Now obviously not all of this is consistent with the SMW maps, but it's just something I whipped up on the spot. Open 3D exploration was the theme of half of these areas and it didn't hamper the platforming. There's also no real empty space between these areas either as one level from a previous game leads directly to another.
The game play would revolve around exploration, finding coins and Power Stars as seen in Mario 64, and stopping all of Bowser's plans by destroying his castles in each of the different kingdoms. Coins can be used at Toad Houses, now modified into shops or minigame areas, to purchase supplies like fire flowers, feathers, or mushrooms. You could also have cosmetic changes in exchange for coins, purchasing alternate mario outfits like the red overalls and blue shirt from SMB1.
