[outofpaper]

Further clarification: the project can be relicensed under a compatible license. This approach would mean that new code is released under the new license, such as the AGPL, while the existing code remains under the GPL. It's a little complicated but quite doable.

[mrbungie]

You need to have a compelling backlog to continue developing down the road or someone can just fork it.

[outofpaper]

WP Engine might try forking it (as they are free to now) but they don't contribute that much to Wordpress as is.