It is already possible by a simple use of copy paste.
- Open the font with the Small Capital Glyphs
- Select and copy them to the clipboard (assuming they’re already in A-Z order)
- Select the lowercase glyphs
- Paste (glyph contours and metrics are copied by default) overwriting the existing glyphs
- Delete the now redundant Small Caps glyphs
- Run the Autonaming wizard
- Save the font with a new name.
The only problem is finding suitable fonts with an OpenSource license that allow you to do this.
FontCreator Professional includes a glyph transformation wizard, which allows you to add Small Capital glyphs to any font that doesn’t have them. It requires rather more work than just running the transform script, but its not particularly difficult.