This has nothing to do with copyleft outbound licensing.
If you have BSD-style outbound licensing and you assume that all inbound copyright is transferred to you, you will wake up in court after you try to change the outbound license conditions of someone else's copyrighted code.
The correct answer is that for any project in which there is no inbound contribution agreement in place, you would have to contact all contributors and seek their permission to relicense.
If you have BSD-style outbound licensing and you assume that all inbound copyright is transferred to you, you will wake up in court after you try to change the outbound license conditions of someone else's copyrighted code.
The correct answer is that for any project in which there is no inbound contribution agreement in place, you would have to contact all contributors and seek their permission to relicense.
Inbound and outbound licensing are orthogonal.