"fast-install" mode in libtool switches the build process in libtool to avoid relinking in the install phase by privileging the deployer over the developer (the upstream developer, not the Gentoo developer). It does so by building all binaries for the final phase, and only relinks them if binaries are needed in test phases. This helps in reducing unnecessary relinking in src_install for most users. This feature will have to be conditionally added like --docdir/--htmldir. Exherbo adds it by default in their src_configure phase (https://git.exherbo.org/paludis/paludis.git/tree/paludis/repositories/e/ebuild/exheres-0/build_functions.bash#n148), which seems to indicate that it is generally unproblematic on a large scale.
Only 6 packages (and no eclass) in the tree are passing --enable-fast-install to econf. This doesn't look like a feature that would merit support in the package manager itself.
I just see that the Council has already rejected this feature:
- New econf options,
The addition of '--enable-fast-install' was opposed because it is
already a libtool default and as such is useless. No arguments
were made against '--disable-dependency-tracking'.
'--disable-dependency-tracking' was voted in, while
'--enable-fast-install' was voted out.
> [...] it is already a libtool default and as such is useless
Sounds like we can close the bug then.