Actually, after a bit of fiddling, it turns out you can use Markdown in an html table cell. You just have to leave a blank line above and below the Markdown elements.
Column 1 | Column 2 | Column 3 |
Spoiler |
SummaryThis text will be hidden |
<table>
<tr><td>Column 1</td><td>Column 2</td><td>Column 3</td></tr>
<tr><td>
[spoiler]Spoiler[/spoiler]
</td>
<td>
[details="Summary"]
This text will be hidden
[/details]
</td><td>
![image|100x108](upload://85Mctmnil2vou0MWjHM7qFPbcr6.jpeg)
</td></tr>
</table>