For historical reasons, rsyslog offers a number of command line options which are actually configuration settings. These stem back to the days of the original syslogd, where the conf file was just a routing table and "all" other configuration was done via the command line. Some of them (e.g. -r to enable listening to the standard UDP port) have already been removed quite a while ago. Now, we are very serious about removing the rest of them.
The main reason is usability. The actual startup command, and thus the options, is usually well hidden in some init-system definitions. So this is highly distro specific and also heavily depends on the init system being used. It is very far from being intuitive to ask a user find that init system config option and set a specific command line option just to change a small part of the configuration -- while the majority of the config stays well-defined and well-accessible in rsyslog.conf and it's helper files.
As such, we will now either completely remove these command line switches or replace them with new configuration settings. For example, a quick poll on the rsyslog mailing list did show that nobody really cared about the -l and -s options (note the absence of replies). On the other hand, we know that options like -4 (to enable IPv4 only networking) are actually being used. For such "known in-use" options we will provide alternatives via the global() configuration object.
So what's the schedule for this? Given the fact that we assume that most folks don't use these options, we target a quicker change cycle than for previous options. The 8.6.0 release, due for December, 2nd 2014, will emit warning messages when these options are being used - as well as telling users they need to speak up if they need that functionality in the future. Depending on the feedback we receive, the options will be removed in 8.6.1 (Jan, 13th 2015) or a later release.