I have recently bought Mathtype to use as my equation editor in Pages but I have wondered about if it was possible to make a shortcut to insert an equation instead of clicking 'Insert > MathType Equation'
After a little research and thinking, I finally found a solution, how to make an equation shortcut for Pages (it requires to have MathType installed btw).
Anyways, go to the System Preferences > Keyboard > Application Shortcuts and hit the 'Keyboard Shortcuts' fan. Afterwards press the little + sign and under 'Applications' add Pages. For the 'Menu Title' go type 'MathType Equation' and finally for the 'Keyboard Shortcut' assign the key(s) you wish to use.