Ian Jackson's general resolution to prevent init system coupling has failed to pass, the majority vote deciding that the resolution is unnecessary. This means that not only will Debian's default init be systemd, but packages will not be required to support other init systems. Presumably, this means that using other init systems on Debian (without using systemd as a base) will not be possible without major workarounds, or possibly at all. It also leaves the future of Debian projects such as kFreeBSD unclear, as systemd is linux specific.
The vote results can be found here
The winners are:
Option 4 "General Resolution is not required"
I wholeheartedly second this. Slackware takes getting used to as there is zero dependency resolution, but (at least for me) that's a blessing in disguise as for one thing, I only end up with the packages I truly need, and two, I've learned a ton over the years about how GNU/Linux really works under the hood thanks to it. I've taken what I learned exploring Slackware and applied it to other distros like Arch and Debian, to fix issues there that would otherwise have required a lot of search-and-try sessions.
As for installing software and libraries, you have the choice of using Slackware binary packages, rolling your own packages via Slackbuilds (highly recommended, and can be semi-automated via sbopkg), using a third party package manager like slapt-get which emulates Debian's apt system, or building and installing from source (also highly recommended, especially if you are interested in tweaking or patching the code before compiling/installing, or if there isn't an existing Slackbuild for that program).
I don't know if Slackware will ever cave to the systemd cabal, but I highly doubt it. And if they ever do, well you can take a lot of what you learn in Slackware and apply it to LFS, Gentoo, and *BSD.