Have used Hugo, and I don't really know what you mean by 'not very easy to customize client side code'. Hugo works with 'themes', which you can either download online, or create yourself. Customizing CSS, JS and even the HTML structure can easily be done by modifying/patching said theme.

Ehhhh... considering what they did to the .NET stack recently (removing dotnet watch from the open source builds to bundle it with Visual Studio and only reverting due to the huge community backlash), I think at least some cautiousness would be warranted.