The 0.X series are based on Debian and uses sysvini system, also all are live disc primary, ...

The 1.X series are based on Devuan and uses sysvinit system, and are install based disc and also package converters.

Gentoo has always been about providing our users (and developers) with
choices.  As long as somebody is willing to maintain a service
manager, Gentoo will host it in our repository along with any
per-package configurations/scripts/etc it may require.

Gentoo actually supports a number of service managers. Our release
media/etc defaults to use OpenRC, though at times alternate release
media using other service managers has been maintained.  Gentoo has
supported systemd as a service manager for years - long before it was
a default on most distros.  Gentoo also supports other service
managers which haven't gotten as much press, and if a contributor
wishes to maintain a new service manager in our repository no policy
will prevent them from doing so.

Systemd has absorbed or replaced a number of previously-standalone
projects over the years (eg udev).  In most cases Gentoo supports the
systemd implementation of these, alongside standalone forks of these
where they exist (several of which were created by Gentoo).  To
varying degrees users can mix and match these as they wish, where this
is supportable.  The default implementations are usually selected by
the maintainers of these components in close collaboration, based on
practical matters such as maturity/compatibility/etc, with the goal of
providing the best overall experience to users regardless of their
choice of service manager.

Gentoo in general tries to stick close to upstream and this is true of
our service managers.  We do not generally apply compatibility layers
so anyone using a non-systemd service manager will not see any kind of
interaction with systemd units/etc.  Likewise systemd users will get
an upstream-like systemd experience and will not see any kind of
interaction with OpenRC scripts/etc.  As a result it is possible to
run a Gentoo system without any trace of systemd, or without any trace
of OpenRC/sysvinit.

As Gentoo has always been about providing choices to our users we
generally do not prohibit software from existing in our repositories
unless it is simply impossible due to legal/etc concerns.  Gentoo
users and contributors are free to use or support the software they
wish as a result.  While Gentoo has certainly not escaped some of the
divisiveness/etc around systemd implementations, argument is actually
fairly rare these days because the various choices individually work
well enough that those who prefer or reject systemd don't really feel
much encumbrance from the actions of the other group.  This might be
why you were under the impression that Gentoo support for systemd is a
recent change - little has changed in the recent past, and there is
little reason to expect any kind of disruption to Gentoo users who
prefer to not use systemd (which is our default anyway).

Keep in mind that this is just a general explanation of
how Gentoo treats systemd (and really just about any package) in
general, and isn't any kind of particular reaction to any issue/etc.
Any policy can be subject to change, but this state of affairs has
been stable for some time so I don't expect that is likely.  And of
course eventually new service managers will likely replace both OpenRC
and systemd - it is just the nature of FOSS to improve, just as OpenRC
and systemd both replaced service managers that came before them.