I definitely like the idea of backup runic enhancement, but once per day is a little meek. Good at first level for sure, but I hope we get a later feat to have it be castable at will on weapons you hold/your body. I mean necromancer, of all classes, can do it at will on any weapon they hold, one at a time. If any class should get that kind of ability, I would hope it would be runesmith. I would also love a mystic armor option as well, for the unarmored runic tattoo trope.
It's okay at 1st through 3rd level, honestly, but then it quickly falls into the problem inherent to the runic enhancement spells: you likely already have the best runes on your weapons the vast majority of the time at levels 4+, which means the spells are functionally useless at levels 4-10, 12-16, and 19-20 (70% of levels). It's especially bad since you are a Runesmith and have multiple other features that make you good at giving out those permanent runes to your entire party.