Having to make new merged layers just to use liquify is a real burden.
I would really like to have Liquify persona work like a non-destructive and infinitely additive process for not only individual layers but also entire image, all the time. That would be something revolutionary.
It's what I don't like about Photoshop - you need to be considerate when it comes to liquify because it only works on smart object that you need to open to fix something after applying liquify. Affinity's Liquify persona could work like a master mesh that just "is" and you don't need to apply it.