Since action economy is concurrent, I have an interesting issue.
I'm running a Bard 4/Sorc 3, and I have one 4th level spell slot. However my metamagic sorcery points only allow me to have up to 3 stored.
In order to maximize the effectiveness of my spell slot usage, when I'm at 0 sorcery points, I want to use the bonus action to burn the 4th level spell slot. This gives me 4 points back, however since I'm a Sorcerer level 3 I can't have 4 points banked.
So in order to not waste the 4th point when I burn that spell slot, I want to use it in the same turn by casting an Empowered spell. If I do this, and since actions are concurrent, I'll have used 1 point, and have 3 left over, which is fine because I can have up to 3 stored.
When answering, please consider that officially you can use a reaction during your action to counter a counter-spell with your own counter-spell and not interrupt your initial action. This demonstrates that the action economy is concurrent in 5e, removing any "stack" discussion from the equation.