I am about to entirely replace OS X with Linux. I am pretty clued up as an experienced Linux user but far from being a true geek.
Mac: I like the hardware but not the OS. So I am not really interested in dual-booting at all.
Current MacbookPro (Mavericks) is a 2012 i5 2.5GHz with 4GB DDR and an aftermarket WD 1TB HDD and Mint 17.1 LiveSession runs rather well.
You have in your possession some nice hardware. You can run just about any Linux system on that.
Also considering a new MacbookPro 15" 2.2Ghz i7 Quad with 16GB DDR, IrisPro and a 256GB SSD.
- Is there any reason NOT to replace the entire OS X?
I believe there are two reasons not to replace your current OS:
1) the hardware does not support Linux
2) you still want to use your current system's native apps
FOSS has thousands of software you can use in place of the apps you are using now. They won't work the same or implement the same features. Some are more stable than others. IF those native apps are of high importance, or you cannot find good open source replacements for them, do not wipe your current system
Another thing to keep in mind is the support level of linux on your current hardware. You may be able to use the Live-session of your preferred Linux OS, but it might not install correctly on your hardware. Dualbooting will ensure that if something goes wrong, you can always go back to what works. If everything works as planned, or works as satisfactory levels, then you can decide on when to completely let linux take over your system.
- Will the Macbook allow replacing OS X?
First thing is to find out if that MacOSX hardware will allow another OS to be installed. The question is yes. You can install Linux on Mac-grade hardware.
- How well does Linux (Mint) handle the Retina display? Will it at least do 1920x1080 resolution, or can Linux go higher?
Depending on the support your chosen Linux system has on your graphic controller, you can either have all or some of the resolution features of your system. Linux upgrades its hardware support database constantly. The generic open drivers that deploys with the more modern Linux systems offers above average support for graphic controllers. If you need to access all the features of your GPU, then it is best to install the proprietary drivers for your system. Should be able to find them on your system's support website.