That’s unfortunate inner-blocks isn’t supported yet. Like you, in the meantime I had to settle for using WYSIWYG editors inside of my columns.
For my column layout, I went with a repeater and styled them to be horizontal. I widened the content area so there is more room to work inside each column, it works out pretty good. I also added a button group for different column layouts and then use JS to automatically resize the column widths based on the layout selected.
Overall I guess I am happy with it.