These are just some things I've been thinking of, so let's see what you guys think.
1.) Project Promotion
One of the biggest issues with Mint, and Linux in general, is the poor reliability of various programs. They're mostly written by people who are writing code on the weekend as a hobby, and there are dozens of different projects trying to do the same thing, but few of them actually do it well.
I think we should begin promoting and funding specific projects that will be used in the Linux Mint desktop. In other words, we'd pick specific projects for various things like a video editor, a music player, an audio editor, a vector editor, photo editor, etc. The reason I mention those projects is that I think we have the useability down for Mint, but we still don't have the incentive for a lot of people to move over to Mint. If we picked projects, stuck with them, promoted them and funded them via donations, not only could we improve the software that we have but we could set the standard. I think funding these projects would make a significant difference in quality.
By the way, if it were me, I'd sponsor Openshot(NLE video editor), Nightingale(music player), Lumiera(video compositor), GIMP, and Inkscape, just to name a few. Actually, I think it would be especially important for GIMP because GIMP still needs real CMYK and float point support to bring more people over to it from Photoshop.
Linux Mint could still remain free, but you would be asked to donate at download time, and the user could see exactly what projects their donation would go towards(vs a nebulous general fund). If Mint were to sponsor projects to improve the Linux experience, I'd happily donate $5 or even $10 every time I downloaded a new version.
2.) Better Tagline
Throw out "from freedom came elegance". To people who understand the need for an elegant desktop experience, this means something to us. But to the vast amount of people out there who could be using Mint, it sounds stupid. I can't tell you how many times I've shown Mint to people and they say "haha, what does 'from freedom came elegance' mean?" Then I tell them, and they're like "Oh, that's nice..."
We need a better tagline. In fact, even no tagline would be better.
3.) Put Mint in control of the desktop environment.
I suggested this ages ago, and I'm glad to see Linux Mint has already done this with Cinnamon. I used to be a GNOME 2 freak and I thought MATE was going to be the way to go, but after using it, Cinnamon is pretty good and has lots of potential. I hope Mint can take it even further. Hopefully, it will become completely forked and will serve and powerful competition to the still awful GNOME 3 Shell.
4.) Make flash easier to update.
Yeah, I know that flash is "going away", but it's going to be around for a while longer and a lot of people still like playing flash games.
Mint did a good thing by having its own flash plugin package, but it needs to be more updated! The flash plugin doesn't have any dependencies(or necessary ones anyway), and there really isn't anything between releases that would break a Linux Mint system. That's because it's just a freaking Mozilla plugin, and I hate having to update the plugin manually. As soon as a new version of Flash comes out, Mint should be right on top of it. But no, it's actually easier for me to just drag it into a symlink in my home folder.
5.) Better taskbar.
What the heck are we still doing with the same kind of taskbar we had 8 years ago? Actually, we had it at least 15 years ago because it's no better than the one in Windows 95! Let's get a freaking dock already! It doesn't have to be anything fruity; just maybe something more icon based like with Windows 7. Yes, I think we should steal the best of ideas from Windows and Mac, and even improve on those ideas. Better yet, this would allow us to get rid of the app launchers on the panel that Windows got rid of years ago, for good reason.
6.) Better "show desktop" icon.
This is something that has puzzled me for a while that Linux Mint has seemed to have stuck with.
Why is our show desktop icon so simple? Why is it located next to the menu icon next to the quick launch icons, when it should be located in the corner? Why can't it be configured to hide the desktop on hover? Why does it even need an icon(yeah, that's less-so debatable)?
I think this point of mine is a little more subjective, but if it were me, I'd get the show-desktop icon out of the way.
7.) Cinnamon menu needs improvement.
Now I'm positive that this is already being worked on, but the mintMenu in cinnamon right now is... alright.
It looks better, but we lost some functionality. Are we going to get this back?
Also, the search box should also allow us to launch applications.
8.) Miller columns in Nautilus.
Mint really isn't to blame for this, since Nautilus is its own project, but perhaps Mint could make an extension for Nautilus for this purpose.
Miller columns are great. I don't like OS X, but that is one thing I loved about Finder. Why doesn't Nautilus have this? In fact, why hasn't Nautilus improved at all? Dolphin has Miller columns, but Dolphin is KDE. Having Miller columns would be a huge benefit, and it would mean one fewer reason for someone to not like Linux Mint.
9.) Installation of cinnamon applets and themes needs to be easier
Sure, I can download plenty of applets and themes, but why isn't the method of installation apparent? It should be possible through just a few clicks.