As per the OP's Q: Yes some of it this would work. Sure would like to see a play session example, though. Some of it has been added to games over the past but a codification of tiers would be a nice starting point.
Elaborate on "codification of tiers," and I'll see what I can do.
For play examples, watch any MMO videos. They get daily quests/awards (session goals), and a nice XP drop upon completing quests (party goals). There aren't really character goals in MMOs, beyond earning prestige or killin' stuff. If there are story goals, they're the waypoints in storylines that the designers create, but those are essentially the same as MMO party goals.
My question would be how is this significantly different from milestone levelling?
I'm thinking milestone levelling = one level per story goal. I'll go into significant differences if you'll go into the definition of milestone levelling.
Fair enough.
I just don't want to see a system which in effect rewards characters who hang back and let other characters take the risks.
This is a valid concern. I, on the other hand, don't want to see a system that rewards the bloodthirsty PCs for starting fights without preparation, and risking others' lives in the process.* The Story Goal might be a balancing factor here - if some PCs clear a major (minor?) story hurdle while others don't, the GM doesn't have to award XP to those who didn't contribute. The nature of the Party Goal is to see everyone work together, and get rewarded together, accordingly. So it would be hard to award some PCs for that and not others, but it's possible.
One of the principles behind the Goal-Based system is that killing stuff and taking the loot aren't what motivate some characters, and they seem to require a certain style of game play, so they shouldn't be the only way to gain XP. If that's what your character is into, your Goals might look like this:
Session: stab the kidney of that hobgoblin sword-spinner who mocked me last session.
Character: calm my inner demons by taking out my rage on others.
Party: Save the village from the aggressive hobgoblin band.
Story: Discover the cause of overt hostilities to the nearby human settlements.
*Not to mention that if XP gets divided amongst fight survivors, some XP systems reward letting your allies die during the fight...