I had already copied the package.json files from the platformio distribution into the mainline distribution. Perhaps there is one missing; I will check again.
I added the nucleo-l010rb board and SoC into Zephyr myself. I have a project on Nucleo-l010rb that compiles and runs through normal Zephyr tools. The major reason I want to use the mainline zephyr source trees is because I am contributing board, SoCs, and other modules to the Zephyr project.
I want to have an IDE with Zephyr, so I am trying PlatformIO. The Zephyr-Eclipse plugin is OK but not great. I think PlatformIO on VSCode could be nicer.