Writer supports Small Caps, but Impress and drawing shapes in general never fully supported Small Caps. The option was available, and the character dialog provided a preview, but Small Caps was rendered the same as All Caps, as seen here.
This has lingered for years and it's not easy as a user to try and manually workaround with varying font sizes because underline/overline/strike-through decorations won't link up, as seen in this example:
but finally for Collabora Hack Week I was able to carve out some time to fix this. So in today's LibreOffice trunk we finally have this implemented as:
In addition a buggy case seen in the preview of double overlines for mixed upper/lower case was also fixed, from:
to:
Also noticed during all of this was the wrong width scaling used for the red wave line underneath incorrect spelling in impress when the text is superscript or subscript so the line didn't stretch over the whole text, as seen here:
Now corrected as:
and finally added was a missing implementation in the RTF export of shape text to allow the small caps format to be copy and pasted into other applications from impress.