There have been several feature requests like this one on transferring reputation onto other SE sites to use as bounties.
The basic argument is sound: I may be knowledgeable on SE topic x, but not on SE topic y. Seeing as I've contributed a lot on site x, giving me an extra incentive that I can use when needing help on site y makes a lot of sense.
The suggestions are all status-declined - if I understand correctly, mainly for the fear of gaming, which is always a clear and present danger. Fair enough.
But how about letting us transfer a very limited amount of rep - for the use as bounty fodder only - say a total of 2% of all points earned? In a very restricted fashion: if you don't have enough points to start the desired bounty, you can fetch the needed rep from one other site, according to your 2% quota on that site.
- You'd get to transfer 200 bounty points for every 10,000 rep points you earn
- You'd get to transfer 1000 bounty points for every 50,000 rep points you earn
- If you never use your transfer quota, nothing will happen.
So for example:
You want to start a 300 bounty on Math.SE
You only have 158 points there
You need 142 points from elsewhere
You have 11,539 points on Stack Overflow. According to the 2% rule, that gives you a 231 point transfer quota, so you can "suck" the missing 142 points from your Stack Overflow rep. The 142 points are transferred; your SO transfer quota remaining is 89 points.
Your 200 bounty on Math.SE can start.
No multi-site transfers, and no repetitions - just this. For every 10,000 points you earn somewhere, you get to transfer 200 points elsewhere once.
That would pretty much rule out any chance of abuse, wouldn't it?
This would not only give an additional reward to users; it would also create another incentive to ask questions across the network.
I could use this right now for a complicated WordPress question I'm about to ask.
I'd obviously like the feature to be retroactive, but it could be either way.
Meta Stack Overflow would probably have to be excluded from this.
An earlier version of this suggestion was about a network-wide "bounty purse" that would grow by 2% of all reputation gained anywhere on the network. I guess that would be easier to implement and a nice incentive to participate in other sites, but as @Purmou points out, it defeats the idea of giving something up to get help.