According to its developers XDAThe Google Play Store it is likely to soon introduce a pay-as-you-go service called "Play Pass". This service will allow you to access all or a select number of apps with a monthly charge.
The first data was found by Quinny899's XDA-recognized developer, who fell on a play store called Play Pass using the Xposed Framework.
The decryption of the Play Pass code implies a subscription service and now another proof of this upcoming feature found on Google Rewards.
Recently a user was asked to "imagine an anonymous application store, subscribed and offers hundreds of apps and games with a monthly subscription. The question also asked the user to explain whether the word "Pass" would be appropriate for such a service.
Considering these two incidents, it's safe to assume that a pay-as-you-go service can soon be available on the Google Play Store. As Google has previously announced research into new products or services under test, it could be the same this time.
However, there is always the possibility that the feature may never see the daylight as it is still in a trial phase.