Many people have improved the LiquidCrystal library over the last few years.
Since about Arduino 0019, which John Raines dramatically improved its speed, added 40x4 format and numerous other improvements, the Arduino Team has not accepted nearly any patches to LiquidCrystal.
I salvaged John's awesome work and renamed it LiquidCrystalFast, which is available here:http://www.pjrc.com/teensy/td_libs_LiquidCrystal.html
Again, LiquidCrystal got numerous 3rd party improvements (apparently all redone without John's work) here:http://forum.arduino.cc/index.php?topic=77120.0
It would be really nice if somehow these many improvements, plus whatever you're going to do, could someday be accepted into Arduino's official version. But before you start, know that LiquidCrystal has been pretty much frozen in Arduino and others have come before you, making pretty awesome improvements to the library which have not been accepted.
Your first step should probably involve communicating with the Arduino Team. You might also review these 2 impressive improvements to the library first. Perhaps if you propose merging all these improvements, they might be willing to accept them?