In many communities that want to have good mods in their favourite games, money for good assets is often the limiting factor.
Since not everyone wants to spend much money on these things, a place to just donate a couple of dollars to a community fund would be quite beneficial. There would be a select number of people (the admins of that group) who would be able to spend that money.
Reasons why this should be on fab.com and not on, for example, patreon:
People like spending money in a direct way, so spending it in the place where it gets spent further. Having patreon page would decrease their motivation to donate since the step patreon->fab exists.
A “funding stretch goal” could be manifested too, with being able to schedule the buying of assets once the required money has been donated. This “roadmap” would be visible to all people to incentivise donating (maybe because they really like the next asset).