TYPO3 Core

The Layout field is still available in FSC based CEs, but it is not rendered into the HTML output anymore.

I can imagine that this was a deliberate decision with the intention that Layout should be used in the future mainly to control rendering right within the fluid templates of the FSC CEs (e.g. for conditional rendering).
But: It would not hurt at all to render out a layout-N class whenever the Layout dropdown is set to something other than "Normal". This would allow for basic and painless CSS based layout changes as were possible with CSC CEs.

The changes to implement this would be minimal:
Change all occurences of...

<div id="c{data.uid}">

<div id="c{data.uid}" class="layout-{data.layout}">

This would also render out the default setting "Normal" as class="layout-0".

If this is unwanted (I would not see why), the 0-case can be eliminated with an additional condition:

<div id="c{data.uid}"<f:if condition="{data.layout}"> class="layout-{data.layout}"</f:if>>

PS:
All this being said I am waiting for the day where all TYPO3 CEs will support a multiselect field where each selection is rendered out as a separate class name. ;D