That's definitely something to be aware of, but the vdev expansion feature was mergered and will be released probably this year.
Additionally, it looks like the authors main gripe is the current way to expand is to add more vdevs. If you plan this out ahead of time then adding more vdevs incrementally isn't an issue, you just need to buy enough drives for a vdev. In homelab use this might an issue, but if OP is planning on a 40 drive setup then needing to buy drives in groups of 2-3 instead of individually shouldn't be a huge deal.