Guys you should try Adshares.net banner crypto advertising to get more users.
No need, duelbits know what should they do with their advertise, they have running signature campaign on here, or even joined on ad space forum, and on other social media, so i think they don't need any site to advertise them atm.
That is a solution. But only as of now, I don't see lots of users complaining or asking duelbits to add more altcoins. Maybe if there's enough users that need it, maybe that's the time they'll consider this request. Or maybe they're working on it now.
Adding or not, it's not a priority thing for them. Adding a new currency i believe it's take a lot of time to do and that's why they just keep ETH & BTC atm