I'm installing 5" solid boards in my house, and in the hallway the boards run such that the very last board would need to be only 1/2" wide, not including the tongue. Is there an issue with ripping a board that narrow? It'd have to be that way for quite some space; like probably 30' or something.

There is no problem with a narrow rip, sometimes it's unavoidable. Just install it and top nail it so the base covers.

You would want to add yellow glue on that narrow piece into the groove, get it snug with pry bar and add temporary wedges against base/wall. Nails will likely split them.

That will definetely resolve potential splitting, ( besides I wouldn't want to disagree with the big chief ).

In my responce , I was picturing myself on the installation. Being the last row, I would follow up with the base, and wouldnt want to wait for glue to set. I usually dont have the splitting problem. Maybe it's my nail gun, or the psi, or the angle I'm nailing, or where I'm nailing, or the brad gauge.

But I agree with Ken. For the purposes of the forum, the correct answer is glue & wedges

What I have done on occasion when encountering this situation is to use glue in the tongue and groove connection between the last full board and the rip. I have on occasion supplimented this with 23 gauge pins horizontally through the rip into the board, but this requires some additional layout and is not really necessary.