This was noticed recently when getting:
https://bugs.gentoo.org/show_bug.cgi?id=420569

Also hit this problem today while trying to bump bluez and noticed we
are using elog messages to tell people to manually install
net-dialup/ppp if they want ppp working with bluez.

I am unsure about the disadvantages of simply using, for example, "ppp"
USE flag to do that. One important disadvantage of current "elog message
way" is that:
1. We rely in people reading the message to get package working ok.
2. If user emerges ppp, it will be recorded in world file and, then, if
in the future he removes bluez, emerge --depclean want clean no longer
needed ppp and then, people end up with a lot of packages they needed to
manually emerge some year but that they problem no longer need at all.

Thanks for your thoughts