There will be pros and cons. because the legislative, historical and cultural context of the institutions and the FS movement in Europe is not the same as the US making joint policy agreements perhaps marginally sub-optimal for FSF and FSFE.
From the perspective of members of both organizations though, it seems
pedantic to have to administer two sets of subscriptions for organizations with identical aims.
A lot would depend on the demand from members for some sort of joint venture on public affairs and also for some arrangement with members subscription payments, which would have to be beneficial in some way for both orgs of course.
Given funding is always an issue for non-profits, there could also be trivial squabbles over resourcing for particular campaigns. DRM might be more of a priority in the US for example, whereas FS in public administrations may be worth targeting more resources on in Europe (or the reverse!).
It could also be that overall each org would experience a downturn in revenue which would not be helpful to either one.
Given each org already has a charitable approach to subs leaving the choice to the individual may be the best strategy.
Data from each org. about duplicate memberships might shed some light on what is really at stake financially and administratively here I think, but making that kind of personal data available would I think also require some form of special dispensation from the members of both orgs?
Mat