I wasn't suggesting that the Assassins are a monk at all, but rather that you could use your "style" system as a way to introduce subclass variants across the board.Now, my first instinct is to disagree violently. My second instinct is to say, "Wait, I think I'm doing what you are suggesting already, but there's some perception problems." And then I think maybe it's just that Reese came into this train of thought on my blog pretty late and is not aware of where I'm coming from and where I think I'm going.
So first, a reminder of some backstory. I've had a number of posts evolving the idea of the class as the answer to "How do I handle problems?" and the principle of each class having only two, maybe three abilities. From there, I moved into rules for constructing variant classes, but I have stated pretty thoroughly that I see most "classes" as really just variations of one of the four core classes. I believe you can get just about any class concept out of Fighter, Magic-User, Talent (Thief, et al.,) or some hybrid of those three, just by changing the fluff of the class abilities and using the same mechanics. Thus, the Thief can also be an Apothecary, a Leech, and now an Assassin; a Magic-User can be a Witch, an Alchemist, or a Psychic, just by fiddling with the spell list, spell trappings, and casting mechanics.
So let's leave aside the question of whether an assassin is or isn't a monk; that's a distraction. The real point is that the Assassin class used the Martial Arts Monk class as a partial template to define Assassin abilities. Both are defined as using Fighter XP, M-U/Thief HD, and both get a combat style as one of their abilities, with the style being improvable outside normal bounds.
What I interpreted Reese's request to mean was that, instead of starting with a limited Fighter and adding a combat style, you could start with a Thief and add a combat style to create an Assassin, which is what I did. Perhaps the suggestion, though, was to not change the Thief at all, but simply give the Thief a combat style. This runs into the way I differentiate between "changing a class" and "adding to a class". If you swap one class ability for another, or swap slower hit dice advancement for an extra class ability, that's a change. The class is still more or less what you started with: the Monk is still a Fighter, the Assassin is still a Thief.
Adding something, instead of swapping, is to me something you do in play, like the secrets for each style, or adding a new style. I wouldn't add an extra ability to a character before play, during character creation. Extra abilities have to be earned.
So, I could see using Reese's approach for a Thief who starts play as a Thief, but who wants to seek out and join the Assassin's Guild, to learn their ways. But that's closer to multiclassing or adding a prestige class; adding an extra ability without that important roleplaying element is more like choosing feats, which is not something I like.