I hear what you saying, but again im sure lots of designers who prefer to keep their addons freeware, will do so and many of them stated they will always keep it freeware as their choice.
This suggestion/idea is already at play when you look at 1) DCS, with freeware simulator and payware content in order to expand the sim, and even 2) FTsim who also releases freeware sound packages but are limited to certain sounds, and for a few bucks a month, you can access full sound packages, so in this sense, if this idea has not spread to variety designer groups by now, then it will eventually, with or without my posted suggestion.
But the suggestion I made specifically for the LevelUp B737NG Series, was aimed at encouragement to continue with updates and work for this fine addon, as we value their work and the even the fear of losing a great addon such as the LU 737. I mean, how many payware addons even, have some of us not purchased and eventually ended up as abandonware and incompatible over time?
So yes, i hear what you are saying that this idea will spark fear of being the end of freeware. But we also need to look at the big picture from a flightsim community point of view, if we lose these fine designers, then we lose the addons too, and how far are we willing to go, to keep them active and motivated to produce more or even better addons in the future?