As suggested by @ennru, we might want to introduce a bug bounty system.
Here is the JHipster story: https://blog.opencollective.com/jhipsters-bounty-system-and-how-it-saved-the-project/
Also please have a look at their sponsors page, that describes their current system: https://www.jhipster.tech/sponsors/
Basically they tag an issue as "bug-bounty" and an amount (ranging from $100 to $500):

Here is the list of issues with bounties so far: https://github.com/jhipster/generator-jhipster/pulls?q=label%3A%22%24%24+bug-bounty+%24%24%22 (However not sure if they have other repos using that tags as well, didn't check)
I am totally open for a bug bounty system like JHipster has, so everyone that contributes can claim money for their time invested, however IMHO I think we should take a hybrid approach. That means that core contributors that decide to work on Play part time or full time, should get paid accordingly on a monthly or weekly basis, in addition to contributors that can claim money for certain issues/pull requests. Based on my own experience, there is always quite a lot of work to do which doesn't get tracked by an issue or pull request, so just paying a core contributor that works on the project part time or full time based on bounties tagged to an issue/pr wouldn't be fair.
(That's just my opinion however).
I had a look at the JHipster payouts and even they did not just pay out only bounties, they did have weeks were a dev was working full time on it:

They did that for a couple of weeks as far as I can see (Also it looks like all of the JHipster core team members are employed as full time devs for different companies anyway).
Compared to socket.io were the main dev gets a monthly payout (they do not have a bug bounty system however):

However, to realize such a hybrid system, we need sponsors that give enough money to make it happen...
As suggested by @ennru, we might want to introduce a bug bounty system.

Here is the JHipster story: https://blog.opencollective.com/jhipsters-bounty-system-and-how-it-saved-the-project/
Also please have a look at their sponsors page, that describes their current system: https://www.jhipster.tech/sponsors/
Basically they tag an issue as "bug-bounty" and an amount (ranging from $100 to $500):
Here is the list of issues with bounties so far: https://github.com/jhipster/generator-jhipster/pulls?q=label%3A%22%24%24+bug-bounty+%24%24%22 (However not sure if they have other repos using that tags as well, didn't check)
I am totally open for a bug bounty system like JHipster has, so everyone that contributes can claim money for their time invested, however IMHO I think we should take a hybrid approach. That means that core contributors that decide to work on Play part time or full time, should get paid accordingly on a monthly or weekly basis, in addition to contributors that can claim money for certain issues/pull requests. Based on my own experience, there is always quite a lot of work to do which doesn't get tracked by an issue or pull request, so just paying a core contributor that works on the project part time or full time based on bounties tagged to an issue/pr wouldn't be fair.

(That's just my opinion however).
I had a look at the JHipster payouts and even they did not just pay out only bounties, they did have weeks were a dev was working full time on it:
They did that for a couple of weeks as far as I can see (Also it looks like all of the JHipster core team members are employed as full time devs for different companies anyway).
Compared to socket.io were the main dev gets a monthly payout (they do not have a bug bounty system however):

However, to realize such a hybrid system, we need sponsors that give enough money to make it happen...