Is the vocative comma a recent thing?
Solution 1:
It looks like we’ve always had it. Look at Luke 18:13 in the Halgan Gospel (reprinted 1842) for example and note the comma after God:
God, beo þú milde me synfullum.
(NIV: God, have mercy on me, a sinner.)
I’m not sure when exactly this was written, but it’s Old English.