I’m divided on this. On the one hand, it might encourage more people to donate, on the other, it might shame low-income people who can’t afford to donate (or don’t/can’t have a credit card) but contribute a lot in other ways.
That abandoned PR by @Stereo seemed like better idea to me, as (if I understand it correctly) it would add icon for every OSMF member (which can be accomplished not only by paying membership fees, but also by instead editing the map regularly).
On the other hand, it is not perfect either. For example, I’ve been (paying) OSMF member for a time, but decided to drop out - as politicking at the time was negatively impacting my health. Nowdays I’m not an OSMF member (even though I qualify for gratis membership), don’t follow regular news and don’t even own a TV - going outside to hike/cycle and map instead. (And as result I am much happier, so I would recommend that to everyone feeling stressed; but I digress).