From what I heard, and it makes sense. Job points will be needed to complete heist. Instead of collecting a van you need for a heist or such you will instead do whatever jobs you choose and the JP will act as the resources for the heist. So before you can even do a heist you have to spend an hour or so playing jobs, this keeps the money from being too fast.
That being said there are two things to mention
1) Will JP be changed to stay instead of returning to 0 when you log off? Wouldn't it suck to get 115 JP out of 130 JP only to log off for going idle because something in RL needed your attention?
2) R* promised that cash cards will be for those people who want to speed through things/don't have enough free time to earn virtual money. Heist will likely be as other have said and unlock via level. People who don't have a lot of free time won't be a high enough level for $500k heist so they need to buy the cards
On another note the heist leader decides who gets the money, so technically a 500k heist could give you very little if you split it amongst 10 or more crew members. Or a lot if you decide to f*ck them over, but I hope that if you decide to f*ck people over and keep the money there's a way to get you back. Wouldn't it be awesome if I'm sitting in my apartment with the 500k I kept only to here BANG! Door explodes and my crew comes in with AA12s and uzis XD.