I have to say letting the OBS believe that he is "working" on their marriage while you know he is cheating is a kin to wanting to wait until after the wedding to tell the bride her betroth has been cheating so as not to ruin the wedding.
It sounds like you know it's the right thing to do so I won't add anymore to that.
It sounds like you don't want any part of (revenge) consequences for OM so I'll leave that alone.
I'm not going to address the link you posted because you've gotten enough feedback. Why you would focus on one WS message when you have so many experienced BS telling you the opposite I don't know. Yes, they have a different views but...they had a different view on their vows too.
I'm only addressing YOU and trying to understand why YOU think it would be best for your relationship with WW if you don't tell. Currently you've only stated
dude will be 100% free to try and pursue a relationship with my wife
as your reasoning. This makes it sound like the only hope you have for reconcile lies with OM not being available.
--WW isn't showing remorse or signs that she wants to reconcile because she has one foot out the door waiting to see what happens with his divorce.
-- With the extra time waiting for OM divorce are you going to try to "win-her-back"? Pick me dance has never worked.
-- do you think the fog is going to lift for WW while she is waiting for OM's divorce?
-- If WW really thought she had a chance with OM she would be pushing you to tell. So they could be together that much more quickly.
You are acting like it's a catch 22. That if you tell the OBS your WW will dump you completely but if you don't tell you WW won't work on reconciliation. The truth is, that she isn't working on reconciliation and while it seems far fetched telling the OBS might be the ticket that turns that around.
-- OM is going to be busy trying to fix or going through a much rougher divorce than focused on your WW.
-- OM might blame your WW for the problems in his divorce/marriage.
-- WW will finally see that they didn't have some fantasy romantic affair-- that they were just screwing up families.
-- The OBS could tell you some major things about OM. I doubt this was his first rodeo.
-- The OBS might make the OM quit his job so you won't have to deal with the HR stuff.
-- You will have someone going through the same stuff as you. Someone that you can get the truth from.
-- You will get to the point of knowing if reconciliation is an option much more quickly.
-- You will no longer be an accomplice. You will feel better about yourself for helping some woman that is trying desperately to save her marriage know the truth about what's going on.
-- If you are being truthful about doing this eventually, you will get it over. It's a game changer she will be angry at you at first but if she is reconcile material she will get there much more quickly too. OM is either going to throw her under the bus or pursue her it would be better for that to happen now than in 4 months so you can get on with your life.
If you have some other reason for waiting or not telling the OBS please let us know. We have seen this time and time again on these boards. Many that don't tell (because they don't want to hurt reconciliation) end up telling out of guilt 6 months later... and dredging up the affair all over again.
I'm sorry, right now it just looks like OM, WW and you are all waiting to see if he gets a divorce so you can decide if reconciliation is an option. It makes it sound like you are fine being WW plan B.