<blockquote><i>What would be exact the impacts to this
The main impact is that it's a different RE language. Some scripts that currently work would cease to function as expected, despite not being <i>necessarily</i> broken by things (with the main portion of that impact being in the different set of backslash-escapes supported).
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<small>A necessary breakage would be something like the syntax for lookbehind becoming used for that purpose. We would not get upset over that.</small>