I can't imagine the Rams are counting on JG to play in the playoffs, nor does any team count on their Back-up for that.
The issue is his regular season stats, if we want to get picky about it.
Look, I'm not some big JG fan. I'm saying sure, he is probably a system QB (in fact almost all QBs are system QBs). But McVay says the systems he has played are similar to what the Rams run. Based on that is a really good back-up for this team, and not some longer term plug-in at some later date. If the Rams were to lose Stafford for the season, then JG isn't going to lead us to the playoffs or in the playoffs.