I'm not sure exactly what you're saying...

I don't have a 100% thought out definition.

However, in some places people can't interact with their government and they still have a small ceremony with some tribal leader or such.

Before Sweden accepted gay marriage and started forcing rules on the church, all pastors could wed people. But everyone but the state church gave up that right so they wouldn't be forced to wed someone that was against their conscience. They will still hold ceremonies but the couple either needs to bring in a priest for a certain section, or go to the court to sign the papers, for it to be legally acknowledged. In my opinion, those people are still married under God after the church ceremony, even if it takes them a few days before they end up filing the legal paperwork.

So, I think there needs to be some kind of commitment expressed, and at least 1 witness.

I'm not sure I understand the "proof of existence on the timechain" part, but it sounds like they'd be marking their commitment in a permanent place, though not with the state, so that seems acceptable and even good to me.