[[Template:t-SOP]]

It depends on neither (look up in the code, I replicated the linking code in JavaScript). But making this change can make migration away from {{t-SOP}} easier, by a simple fixed text substitution (s/{{t-SOP/{{subst:t-SOP/g and save)

Oh, I see. That isn't really needed though because I already have a bot script that replaces {{t-SOP}} with {{tø}}.