I think this is a great idea as a non-binding way to let our representatives know how those of their constituents who care, and thus are most likely to vote in a real election, feel about various issues. Representatives should be able to voice their opinions about such issues too, in the same forum, and should be able to vote however they want regardless of the online polling results.
The only other thing that I would want in an ideal online representative democratic system would be a place to post ideas for bills that I think should be taken up. These could then be voted on by constituents too and maybe taken up by our representatives. As someone with no political connections, I otherwise have no idea where to start presenting such ideas.