The title says it all, really - should we have a tag for physical organic chemistry?
I think there is absolutely no doubt that it satisfies the usual metrics in terms of scope, etc. and currently there is a risk of some questions simply not fitting in too well with other tags (see How are $\sigma$ and $\sigma^\pm$ determined in Hammett plots? for one example).
My main concern is that it could potentially be misused, since it contains three(!) broad keywords.