I'm with you on the dating thing, well, in general I have a hard time "bringing things up."
If she's already talked about being intimately involved maybe you could use that as a segway into polyamory. My current SO, before we started dating would fairly regularly suggest that we make out, along with reiterating that "My wife won't mind." And clarifying to her that you are interested in her but no, you're not leaving your wife or unhappy there is good, just in case. Keep us posted!