A personal FSP bank is just that, PERSONAL.
Being able to withdraw from a guild FSP bank is not personal. The person with the permission (if it were ever granted) may well have not contributed ANY fsp ...
Historically, fsp withdrawals from the guild kitty have always been denied as a measure of "safety" for the guild fortunes - I personally see no reason to change it.
If guilds need fsp's for new gear, or to pay for gvg'rs, or whatever, then the founder can just ask for donations from members directly, rather than into the upgrade "bank".
Pardoux... just more "brain (or lack of) storming"... I recently did exactly what you mentioned for some forging.
This is definitely not something I would prioritize. However, what would you think about the possibility of two Guild FSP banks?
The idea is one that is protected with no withdrawal capabilities and one that has a withdrawal option (GF restricted or permission-based)? Think that "might" be interesting and take care of the "work"...
Again, definitely not a priority and if there is some discussion out there... would love a link to get more info.
Thanks.