Starting up a custody battle would only be out of spite and you know that.
My R's with my 3 older kids were ruined because of the custody battle, it is also the reason I am divorced, as prior to that we were looking at houses and he even told his mother he was moving with me.
I had a baby - my last pregnancy - that died because of that custody battle and the stress. I have nightmares all the time about the kids, I'm too upset most of the time to even speak to them on the phone, my impression of Andy as a father has nose-dived, my DD1 barely speaks to me anymore and I find myself DB'ing with the kids too.
Most of the people who know me don't even know I have 4 kids as I'm too ashamed of being non-custodial to tell them.
I was mother of 5 and I became mother of 1. I very nearly lost her too and all of her babyhood was ruined for me in a haze of court fighting and the fact that every time he had visitation, I was afraid I would never see her again.
He nearly got sent to prison, the kids nearly got put in foster care. I lost ALL of my extended relatives in this court battle as they couldn't handle the stress and turned against me.
Most of the friends I had during the M I no longer have because they either took sides or I cut contact after I became non-custodial.
My DD2 was in therapy, threatening to kill herself and I can't even have any modern photos of them about the house as it just damn hurts too much. I have plenty of pictures, but they are all old, from when I still raised them.
The custody battle destroyed my entire family and I can tell you something else, Gabriel, most women aren't as tolerant as me, nor do they try so hard or forgive so long, and it's been 3 and a half years. If you do this custody battle, your XW will not respond in the way I did to Andy and I can almost guarantee you won't get any second chances or opportunities to DB.
Andy could worm his way back in because I showed unconditional love and I forgave him for whatever he did, even with the kids. I just know she won't forgive you for trying to take S5.
So if you want to destroy your entire family, any chance of a friendship with XW, your S5's self-esteem and everything else, go right ahead, but I'm not going to back that.