Wuxia is something that martial characters should not be able to represent, typically. (I'd actually say Wuxia doesn't belong in D&D, but I don't mind a non-intrusive source book .)
I disagree with this a lot. Wuxia should be an option for high-level Fighters. A 15th level Fighter should be able to
wreck the same flying demonic horde that his Cleric and Wizard buddies do-- whether he does that by knocking them out of the air with his crossbow, daring them to come back down and fight like men, or just Peter Panning his ass up there to stab them with his sword should be a stylistic decision.
I agree that low level mundane characters should be limited by physics. It might be Hollywood physics, but, still reasonable. But high level martial characters should get a touch mythic. I have no problems with that 15th level fighter obliterating armies and punching through mountains, just because he's that mythic.
I think this is a 'calibrating your expectations' sort of thing-- we really need to sit down and figure out what levels mean what in terms of what kind of power characters (from all power sources) are wielding. Set benchmarks. Figure out at what level divine ascension is the next logical step, and then scale your characters backwards from there.
For instance, I consider 1st level a good benchmark for 'exceptional talent': a hardened combat veteran is still 0th level. A 1st level Fighter is the fencing academy's most promising student or the farm kid who killed half a dozen goblins with a pitchfork in his first battle.
I'm a
Rules Cyclopedia kinda guy, so I like the idea that 36th level is when you start playing a different game entirely-- after 36th, you're no longer advancing in character levels, you're advancing in deity levels. A 36th level Fighter might not be as powerful as the recognized God of War in his particular milieu, but he isn't a servant of the war god; he's either an ally or a rival.
Consequently, you divide that in half... 18th level is about the threshold between 'super hero' and 'demigod'. This is where Clerics and Wizards get 9th level spells, this is where 'immortality' might show up as an actual class feature, and so forth. I'm thinking that 'immortality' shouldn't be a class feature... so much as just a given for what being 18th level means.
Cut it in half again, and you get 9th. 9th is where details like physics just don't matter so much anymore. This is the level where Clerics raise the dead and where Wizards get to decide whether or not 'gravity' is a thing that applies to them anymore. This is the level where I think Batman should be able to breathe in space and learning to fly is a matter of throwing yourself at the ground and missing-- you shouldn't
have to do these things, but they should be options.
Cut that in half one more time (let's round up) and you get 5th. 5th is the level the magic happens-- no, seriously. 5th level is where 3.X characters start breaking real-life world records without trying. This is where a good Dex score and max ranks in Acrobatics part ways with reality and where swimming in plate mail becomes a viable option.
D&D needs to be able to support all of these levels of play. And it's never really done it well-- there's always way more support at the bottom levels than the top, and before 4e the game only got up to around 12th before the math stopped making sense. The main issue, though, is that some people are only interested in 5th level D&D or 9th level D&D-- a perfectly valid matter of preference-- and the D&D rules have just never been designed to
linger at a given power level.
What I would like to see is something like E6 as a core rules variant. But instead of having a level cap at 6 and then only gaining skills and feats thereafter, you take advantage of Next's flat math: you gain theme choices and feats normally, but your maximum
class level in a single class is X and your effective character level (for ability boosts and theme prerequisites) is equal to your character level times X/36.
And, seriously, if that doesn't point out just how absolutely god-awful 3.x multiclassing would be in this system-- and the need for a real rules fix rather than a bunch of PrC patches-- I just don't know how to explain it any better.