Comment 9 for bug 1636666

It seems likely that Ubuntu will have to support/ship both PCRE and PCRE2 before long. At least some other distros (Fedora, Gentoo, Debian) appear to be doing that already.

As mentioned above, for packaging purposes PCRE2 is effectively a new project, *not* a new version of the previous PCRE. The APIs are completely incompatible, and the previous PCRE is still getting bugfixes and seems to be supported/recommended for existing projects that already use it. There are a number of largish projects that don't support PCRE2 and presumably won't anytime soon (e.g. https://bz.apache.org/bugzilla/show_bug.cgi?id=57471).

So it seems unlikely that the whole package ecosystem will ever simultaneously support a single incarnation of PCRE, allowing Ubuntu to ship only that one. Already some packages don't support the old incarnation, and as mentioned above, it's likely that some will never support the new incarnation.