It is not clear to me what you are looking for. You touched on a mixture of different problems including generating weighted graphs (with what precise constraint?), the bad time performance of “simple.no.multiple” and sampling bipartite graphs with given degrees.
If you can give a mathematically precise description of what you are looking for, ideally with a concrete example, then we can tell you whether this is already available in igraph, or if not, whether it is easy to implement with the current functionality.