I'm currently on 2.1.8, and the addChild signature is actually public function addChild($alias, $block, $data = []), where the alias and block are strings, and the createBlock is the first thing done inside. So you call it like $this->addChild('my-alias', 'Vendor\Module\Block\Name').

Great suggestion, this does work in that it fills the dropdown with the stores. However, it no longer shows the store before activating the inline editor. I tried adding the class back to the column, and moving the options to different levels, but they seem to conflict. I'm only able to get one to work at a time--either the stores display in the grid on load, or they display in the dropdown select on edit.