Instead of making progression purely instantaneous, like XP-based systems usually are, the progression I have in mind, offers an addicitive duality.
- Progressing certain aspects of the game by successfully doing it - feats of skill - like leveling up swordplay by slaying enemies with swords, or unlocking new guns and attachments by shooting dudes dead. But wait, that's only one side of the coin.
- Additionally reward the player with 'Training Time Allotment', rather than straight-up XP. Training Time Allotment is being used to manage progression whilst not playing the game. So lets say I play a lot of Battlefield, I earn lots of Training Time Allotment, which I can use to progress through certain carefully chosen aspects of the game, whilst no playing it.
Lets say I play a lot of Battlefield, I earn lots of Training Time Allotment, which I can use to progress through certain carefully chosen aspects of the game, whilst not actually playing it. Like in Battlefield 3, there's a weapon-specific progression, governing attachment unocks. Imagine the game lets me spend Training Time Allotment on some new weapon I just unlocked through regular play, so the next time I'll play the game, I will have unlocked some basic attachments for it, during the time I was not playing the game, like when I was at work or school or in bed or whatever.
Every time I stop playing a game using 'Training Time Allotment'-like progression system, I get to manage offtime progression, and I'll always have something to look forward to, when I come back around to playing the game.