The biggest usability improvement to the EPGs on all platforms would be to implement switching between HD and SD versions by a toggle (one of the coloured buttons perhaps) on the same LCN rather than cluttering up the EPG with duplicates.
The Virgin EPG is particularly awful but Freeview and Sky aren't great
Virgin in Scotland (and I believe NI and Wales) have simply ditched put BBC1 Scotland HD on 101 and STV HD on 103. Channel 4 remains an outlier with the SD version still on 104.
That said I was also informed this was perhaps more due to lucky accident / Virgin's incompetence than design. See also their mock designs gallery of channel logos