Not likely. Nintendo can't just make a demo, fully develop it and then begin from scratch at the last minute. It's just not physically possible.

Let me explain a few factors here:

The reason why Nintendo reduced the quality of NSMB's sprites is due to the DS' limitations. The unit runs on two processors: one that is the ARM9 and one that is the ARM7. The processors round to 4 MB of RAM and 256 kB of Serial Flash Memory, which make game experience VERY limited. Sure, in the beta NSMB everything looked better and had better graphics but did you think of what would've happened if they continued making sprites that good of quality?

If Nintendo was to continue developing the beta NSMB into the final product, chances are that the DS would have not ran the ROM. You see, the game had REALLY good graphics and high quality graphics equal more memory. Nintendo HAD to have already begun the final version before the beta version of NSMB was shown to public. Would you prefer quality over quantity, or quantity over quality? Those sprites must have lagged the DS if they had over four levels, considering the fact that the DS can't even render 3D objects that good.

I'm pretty sure Nintendo did make those nice looking 3D koopas and goombas but simply removed them after the production of the final version of NSMB and after they realized that they couldn't include it in-game.

You could install BootCamp on OS X. I know I've done it before when I used to have a MacBook Pro.

Boot Camp allows you to install Windows alongside OS X on your Mac. Only one operating system can be running at a time, so you'll have to restart your Mac to switch between OS X and Windows. If you've ever dual-booted Linux on your Windows PC, it's basically like that.

Uh, isn't this against the rules?

I thought I only played Geometry Dash.

I've completed:

Stereo Madness

Back On Track

Polargeist

Dry Out

Base After Base

Can't Let Go

Jumper

Time Machine

Cycles

xStep

Theory of Everything

The rest are all incomplete. Most levels I finished have all star coins collected, except on Cycles. I didn't get one at all for that level.

Don't do that. Many have gotten in trouble for doing that. If you change those credits its like saying that you own the game, and that you made it, which you didn't.

I would highly suggest to add right next to the credits your name. It'd look something like this:

I'll believe it when I see it.

I agree. Finding someone without thinking that they are the best, and simply helping out a community is really rare.

I'd like to help. I may not be much use in coding in C++, but I may be in some use in documentation. I could be in charge of organizing, and making it easier to read.

Sadly,  Dirbaio doesn't come online very often.

Have you ever considered your existence to be a mistake?