At some point (software upgrade) this feature was removed, maybe because most people are using LiveTV or Roku LiveTV to get the free streaming channels.
However, I would like this looked into. My antenna channels are not showcased at all without going into SETTINGS -> TV INPUTS -> LIVE TV -> MANAGE CHANNELS -> HIDE STREAMING CHANNELS
Before the update, the antenna channels would be the lowest ones (streaming starts around channel 115) and they were in their own category (I believe it was called "Antenna").
NOTE: Doing a re-scan of antenna channels will populate the Roku software with the channels and, once deselecting the HIDE STREAMING CHANNELS, will allow both streaming and antenna channels to be visible in LiveTV.