Idea is good, but i would rather go for leave HP as it is, then, after 24lvl, you get, for ex. ~2HP (or even 1HP) bonus per lvl. Small, but after some time useful bonus so people can participate in fights on 24lvl, but will have some advantage if they stick to their characters longer.
Personally, as it was proposed some time ago, i liked idea of making fight/craft perks, one after one, for ex. after each 2lvl (2nd lvl crafter perk, 4th lvl fight perk and so on), but its what i would rather do, not nessesary imho.
Stop saying about troll builds - its completely different case. Stick to the subject since its good idea to prevent alting, which is pain in ass for everybody and ruining the game climate since everyone is obligated to do it to prevail.
I personally believe that all features allowing troll builds will be eventually fixed, its a matter of time.
Also: to reach 24lvl you need 276k exp, to reach lvl higher, for ex. 99, you need 4851k exp - its really hard to achieve in the way it is now. Someone will have to calculate which lvl is most optimal (when you got all useful perks/all skills spent), its not said it must be 99, it can be 50, or just make it infinite (which is worse in my opinion)