The HD500 is primarily a device intended for six string guitar, but it is possible to get perfectly acceptable bass sounds using it.  i have done it as have some others, but to be fair I'm not a bass player but I do know a good bass sound

People have asked about additional amp models and bass has been mentioned more than once as have acoustic amp sims.  Line 6 will be aware of these requests and hopefully they will be developing some additional amp models , but no-one knows for sure if or when they might make any additions, so we will just need to wait and see.  Line 6 will never comment on their plans for their product lines.

Nick