With the current specification, there's no way to have a table cell behave as a flexbox container while still behaving as a table cell.

The only values of the "display" property that make an element act as a flex container are:
flex - for a block-level flex container
inline-flex - for an inline-leven flex container.

However, table cells have unique properties that neither "block" nor "inline" elements have. If you want a table cell to behave as a flex container, you would have to set its "display" property to "flex". However, this will mean it will override the value "table-cell", and hence the cell will stop having the properties of a table cell as seen "from the outside".

The most obvious consequence is that the total height of the cell won't expand to the height of the tallest cell in the same table row.

This is an incredibly stupid flaw in the specification. There should be at least one more value, "table-cell-flex", which would behave as a table cell "from the outside" and as an flexbox in the inside.