As I understand there will be a couple of computer terminals available and assistance from an immigration department officer. I can only imagine how the queues will be for this, so I think anyone planning not to do it beforehand should allow an hour or two going through immigration, but at least your luggage will be waiting for you!
So where's the threshold? Ten years together? Thai women are incredibly patient waiting for the goose to lay the golden egg. I think you'll find there's more scam marriages in these situations than genuine. I'm happy to remain single and live with my lady. It's no hardship for me to go once a year to immigration to extend my stay
You do realise just about every country in the world operates similar systems? How many scam marriages would there be in Thailand if the government just threw open the doors to anyone married to a Thai? I wish other countries would adopt the "check in" every year to make sure couples were still actually married and living together