Flexible payment models for apps

Introduction:
Everything is not black and white (free and paid). Sometimes, its better to be grey. Some open-source developers want to receive money for their apps, but at the same time, they want them to be freely available to those who cannot afford to pay. (Exactly the same as Luna's distribution model - http://imgur.com/A9J0mRa,VfaGVcM#0 )

Proposal:
1. Such a feature should be made opt-in for developers. They could choose to sell their application in more traditional ways with fixed pricing if they so wished.
2. Developers could set the default figure to whatever they wish (eg. $5.00), but users could choose to pay more, less or even download the app for free.

Why its better than a straightforward 'donate button':
A 'donate button' brings bad connotations to users not afflicted with the 'open-source donation-based philosophy', and at its worst, it would appear as 'begging'. "Pay-what-you-want" is better and it gives the impression that the app actually costs x-amount of money but you can get it for a cheaper rate (as opposed to "donate" which gives the impression that the app is meant to be free, but you can give your money away for no reason if you want to)