Personally...I don't see how anyone who would take an hour to research the history of the Catholic church could think seriously about joining them with the view to being part of the One True Church.
If you wanna join just to get a free sip of wine and a bite of cracker, well, sure knock yourself out. But if it's about the tradition and the grandeur and the architecture, you don't have to be Catholic to enjoy it. Anyone can pay their money and tour the Vatican and all the other Holy sites.
Touring the Vatican actually caused a Catholic friend of mine to question the motives of the church. He saw all the history, the hundreds of years of marble, granite and gold churches. He saw the millions of dollars in artifacts and art. He then wondered why the church couldn't have used all that power and money to actually help the poor and needy over the centuries instead of amassing one of the largest money coffers in the world.
As far as a former JW joining any other religion...about the only circumstance that wouldn't puzzle me was if a former JW joined a local, neighborhood church that isn't part of a larger organization or church body. If there is a God, I'm sure he would visit that kind of church before he went to see the Vatican, the Southern Baptist convention or any 'mega-church' organization. If Jesus was his son, that's the kind of people he would be drawn to...the simple people who worship for the sake of worship and not for the sake of money, power or fame.
I like what Johnny Cash said about churches...he said he felt closer to any supreme being by being outside in nature and seeing the handiwork of his creator. There was a spiritualism in being alone with nature to him. He didn't understand why people felt the need to go inside a closed up, man-made building to get close to God. Something to think about.