That’s how I read it, and that would be an improvement in that authors could specify a more useful tab order more reliably.
But I think a more useful approach would be allowing for non-linear navigation - Hyojin’s spatial navigation proposal (discussed earlier in this discourse) was discussed at TPAC - rough notes from breakout, slides.
There are interesting combinations beyond horizontal/vertical. In effect we already have this in some cases like menus,
aria-flowto, screenreader special navigation modes, etc., and making it work consistently would be helpful. This is especially useful for graphics - flowcharts, circuit diagrams and so on often need it to make sense.
Current approaches are pretty clumsy for both authors and users. In particular they lack predictability for users, and authors are stuck trying to pick an existing paradigm where there isn’t an obvious match or doing stuff that is extra baroque…