Agree with stamas47, it's better to continue work on Lazer.
New big HOTFIX changes, as like as i see #2 point, always produced new bugs (small and big ones). Especially since Lazer is planned to use an entirely new renderer it's just unpleasant waste of time. 2-3 weeks, which #2 could took, also might affect a lot emotionally. And it is very difficult then reconfigured back to work on Lazer, i think.
p.s. I suggest the #3 point. Return to this question only after new Laser's renderer will be presented and worked. And then create, for example, new separate Phaser2-Pixi4 branch just to keep the refactoring in some "sandbox" place.
p.s.s. As i know, Pixi's main developer said (somewhere in one of the topics in this forum) that he has no much time to maintain his stuff. So Pixi v4 can also bring more other bugs...