[yorwba]

In the worst case yes, since that might change the number of words that fit in that line, and that would mean exchanging words with the line before or after that, leading to a cascading effect.

However, you might find that many of the old linebreaks can stay as they are, so I'd expect reflowing to be faster in practice.

[amelius]

I'm thinking the algorithm will then not be able to provide a responsive UI in all cases, so perhaps browsers should allow for a temporary suboptimal rendering.