Hi,
I can understand the logic for moving away from the word fellow, but I think the word "supporter" might not be ideal either. One challenge with the word "supporter" is that it implies supporters are on the outside of the organization.
If we accept that Fellows by and large consider their involvement in the FSFE to be a monetary one, then it follows naturally that the voting turnout will be lower, and indeed, that "fellows" are somewhat "outside" the organisation.
There is some basis for this conclusion: in 2014, we did a stakeholder survey as part of a strategy group work. One of the questions asked was "How did you participate / contribute in FSFE?"
Among the Fellows, about 80% answered "Donation" to that question, and the rest "Volunteer". So the active volunteers in the group of Fellows is about 20%.