I DECLINE. You do not need Hard mode and Nightmare Mode seperated, it's perfectly fine as it is.
Compare to a certain Massively multiplayer Online Role-playing Game (World of Warcraft) Owned by Blizzard Entertainment
WoW share same kind of lock out for their raid dungeons with normal/heroic 10man & 25man. Big difference is...
WoW: you got a decision of either 10man normal/heroic mode or 25man normal/heroic mode.
SWTOR: Story mode is seperated from Hardmode/NightMare mode because SWTOR has 3 Level and 2 of them high levels separated from that 1 low level.
^ WOW use to have similar lock out where u were able to do both 10man & 25man (either mode) back in Wrath of the Lich King.
Bad news, back on page 4 BioWare said they are going to separate them eventually, its a technical limitation based on who they originally made them, not a philosophical one based on a designed they wish to have.
Sounds like technical hurdles are enough that it won't be very soon, however.