Okay, so I had a dive back into D&D 4E reading the three "Power" books I bought recently. Old School Hack, which is the huge inspiration for my Neo School Hack, borrows a bit from 4E in the Talents which each character class gets. In the original OSH and my NSH each class has six unique talents. To that I've added separate races which each have three unique talents.
When a character levels up they get to add 1 to an attribute, plus gain either a talent or a hit point. Characters may multi-class by taking talents from other classes, with the restriction that they may not have more cross-class talents than talents from their starting class. So with six base class talents, three race talents, and a maximum of six cross-class talents, there is sort of a cap of 15 levels. Yes, there will be boring "empty" levels where the character gains a HP rather than a talent. But a maximum of 15 levels isn't necessarily a bad thing. Early editions of D&D (and modern OSR rules like ACKS) run out around 14. So a cap of 15 levels is well in keeping with the spirit of the rules.
But I'm not sure whether I really like the idea of characters essentially being forced into multi-classing. As a fighter you'd have to scrounge around to keep to only fighter-appropriate talents from other classes to stay "pure". And then there's the problem with wizards learning spell-talents from grimoires. Wizards have a talent which allows them to gain to get access to a new six-spell grimoire (each of which costs a talent gain to learn). So they can keep leveling for as long as there are more grimoires to acquire. None of the other classes is that open-ended.
And clerics get their basic six talents plus access to the six domain talents for their deity. If the domain talents count as class talents (which I suppose they could), then that's six basic talents, six domains, three racial, and up to twelve cross-class. So clerics can keep gaining talents for 27 levels.
And alchemists have lots and lots of sub-talents to explore as they level up. The druid class I'm working on will have a couple Circles of six talents which are a bit like cleric domains.
Hmm, okay so there's a bit of design imbalance here. Obviously there are two approaches to re-balancing things: limit the more open-ended classes or provide more talents for the other classes. Re-balancing the problematic classes can be accomplished simply by treating the class-specific domain/spell/circle talents as cross-class talents. But that still leaves the other classes with fewer options to have fun with. Eventually I should look into providing all classes with a couple additional six-talent sets of talents, like combat style schools for fighters. The character could buy into the class sets in the same way a wizards buys into a grimoire.
But I'm really torn about adding so many talents--yes, we're talking rules bloat here. One of the charms of Old School Hack is its simplicity. Players can review all the classes, make an informed decision, and jump into play with a character very quickly. My Neo School Hack rules take the lovely simplicity of OSH but add bulk in the form of more classes, races, and talents. It's still very simple mechanically but a new player has many more options to review before deciding on what to play, or before even deciding what talent to take on leveling up.
Overall I'm coming up on the last of my work on NSH because I've finalized what I want to have in it and because I want to place a hard stop on rules bloat. All I have left now are the final two classes: druid and ranger.