Not a bad option to consider, but that itself has some downsides since it may not be possible to switch between functions and have all the pins stay connected.
As a test I commented out the yintersect line and returned 0 for that variable and it made no difference to the instruction count. Not that everything you do is properly counted but it may not be enough savings to warrant a separate node.
With Just parallax (no PDO or shadows), it’s showing as 174 instructions right now (with static lighting).
Using PDO the automated way kicks it up to 226 which is crazy (remember that requires 4 texture lookups: ddx-uv, ddy-uv, ddx-world, ddy-world). If you specify the UV-world size manually that brings the PDO cost down to 211. It still seems like a lot. Maybe it is not able to reuse much of the work for the pixel depth offset…