What problem does banning PrCs solve again?
Using the core classes - none.
But this discussion is about improving the Monk.
The PrCs in the DMG at least make you trade something for what you gain - from level 1. As things stand now, there are too many PrCs that grant benefits without making you give up on anything in return, which makes their selection a no-brainer and just emphasizes how badly designed a given base class is.
My usual is mixing a Dex/Wis/Con Monk with PsyWar or some kind of arcanist, the Lucid Cenobite or Kensai PrCl, and adding a polearm.
Which just emphasizes this topic.
A decent base class should stand on it own and have enough worthwhile features in each level that exiting to another class would make you lose something that you'll miss, and not just be viable as a jigsaw piece.
Then how would a player know if he's selecting the right feats etc. to qualify if he can't peek at them in advance? I mean, who takes Dodge on purpose?
You see, that's another problem I have with many PrCs - WotC just presented them to justify lousy feats.
In the age of the web, hiding PrC details from a player is not really an option.
However, in my view, a player should focus on what kind of
character s/he'd like to role. The DM should offer several progression choices to make the player's vision come to life. Only after several levels have passed should the DM make PrCs available - if it's truly necessary for the type of
character the player envisions. And when the need arises - retraining should be allowed.
Anyway, my main point (again) is that a base class should stand on it own.
A PrC, in my view, is about making a direction change, not just amassing MOAR POWAH