I have 2 thoughts on this, Obviously one is this might have to be account wide yet still faction restricted friends list. You shouldn't be on a pub toon and be able to see imp friends online anyways makes no sense there. Also having a imp side credit spamer block on pub side does nothing but waste a slot on the ignore list and vice versa.
Second in regards to a possible privacy concern give each to the ability to login in a sorta stealth mode that block friends list. Of course another idea is to use the ingame AFK tag.
With those being said an account/faction wide friends/ignore list is way overdue so.
/signed