I like the frickin alignment restriction! All WotC needs to do is introduce a "martial artist" specialty (which dovetails with the monk as default) and you can have all the fighter and rogue martial artists you want.
I think sometimes I like alignment restrictions too, but not so much in core classes, and especially if the classes are supposed to be versatile.
Now I don't want you to agree with this, but IMHO a Monk class would be great if it would be versatile by offering different philosophies (in a campaign setting, these could be tied to specific monasteries, but this is perhaps not very feasible in a settings-free core book). Just like Wizards have Traditions, Fighters have Styles etc., Monks could have philosophies
roughly inspired by Shaolin temples, Zen buddhism, Taoism, something related to Hinduism, Shinto... and this could be reflected in different mechanics: "ki" for some, meditations for others, even spell-like abilities for someone else. If this was the setup, there really shouldn't be any alignment restriction on the
whole class, perhaps on some of its subchoices.
Otherwise if the Monk class is not versatile, it could just become a Fighter's Fighting Style: it already uses the same ED mechanics, and "ki" could be a Specialty with "Lawful" as requirement for its feat.
But if you want ki abilities, unarmored AC, and the like, pony up and play a lawful PC.
I really don't get why you believe in this. These are abilities that have absolutely nothing to do with alignment. In very general and simplified terms, "lawful" is someone who believes in authorities, social or universal, and that law & order is important in both society and the cosmos. "Chaotic" is someone who generally doesn't value authority, and favors freedom over law and change over order. These are all ethical or maybe even political ideas, they make sense in terms of connections with the rest of the world.
The dedication and discipline needed to learn martial arts actually require you to actually spend a great deal of time looking at your inner self and practicing/experimenting on your own, and then with your peers. Of course you normally have a "master" to trust blindly, but this is not enough to actually
require you to be lawful towards
everyone else. We might have a certain image of monks temples in the real world which are very regimented to the point that a non-lawful character may feel it unbearable to live there, just because he would dislike strict hierarchies and invasive rules, but this doesn't have to be the case. There are aspects in real-life or fiction martial arts that suggests a more chaotic approach, such as some elements in Bruce Lee's philosophy of Jeet-Kune-Do, or the Drunken Master fighting style.
Bear in mind the monk, sorcerer and warlock aren't as customizable as fighters rogues or clerics. That's fine. You are "specializing" and that limits a few of your choices.
Well but you have to admit that an alignment restriction has never been a very good balancing factor... to some people such limitation is moot (they'll say ok and proceed to roleplay how they want anyway) and to others is a painful restriction to an otherwise perfectly reasonable character concept.