We all know today the devices have different ppi. Traditionally a pixel is a point, which is 1/72 an inch. But today, iPhones have 326 pixel per inch why the point should remain the same for typography practice (12 pt is readable on a desktop monitor but would be too small for iPhone, instead we need 54 to 55 pt on the art board).
This is bad because if I design for multiple devices, I have to change the typography across the art-boards to match similar visual outcomes. Photoshop has provided solution to this issue a long time ago. I wonder if there is some hack we can do to accomplish the same solution in Illustrator.
You can always design in absolute pixels since your monitor and your devices will never have the same pixel density. For example, you could design everything in xhdpi and therefore maintain the same size throughout. Googles holo templates for example work that way too (but in mdpi). The only difference that you'll experience is that your desktop won't show it in the precise density. But since that's impossible anyway I wouldn't worry about it. And you need to test your designs on a device anyway. So set up your artboards to match the testing device and you will always have a correct preview on it.
Have a look at googles samle files: https://developer.android.com/design/downloads/index.html