I wouldn't mind seeing a "Class" system that starts out as a "Skills" system. I.e. you learn skills in order to qualify for a class, much like you apprentice in order to enter a profession. Once you have a class to specialize in, your rate of progression should improve. But you would have the alternative to just keep following the skills road for greater diversity in your capability.
So... you'd qualify for a class at around level 3-4, after completing the prerequisites and training. Until then, you're just an adventurer slash apprentice.