The shod vs unshod has been an ongoing issue for a VERY long time. After riding for a few years I was given my first horse (a 6 month old QH filly in 1971 or 72). I refused to have her shod and thankfully was supported in this by my grandfather, who'd kept unshod horses before.
I was told for at least 3 years by almost everyone, including my vet, that I was going to ruin my horses feet. After about 6 years at least my vet stopped and admitted that my horses (there was more than one then) had the best feet of the horses he looked at.
Now having said that, my horses had always been procured young (two years old was the oldest) and none had ever been shod (the term I hear used a lot today is "barefoot"). I do know that horses that have been shod can have issues when issues they first start going barefoot. I have since purchased horses that were shod and in some cases it's taken months to get their feet corrected. My filly has a split that formed from where a nail from her last shoe was put and I'm having to work on a hole that has formed there going up into the hoof. It could take some time for that to heal and grow out (nothing like having to pick out a hole every few days and repack it with cotton soaked with tea tree oil)
My experience, based on my horses and some other unshod horses (since it's becoming more popular in recent years) vs friends and neighbors have shoes on their horses, has been that horses feet will do better if unshod. You'll hear no shortage of people who will say otherwise, but 40 years of never owning a shod horse has shown me otherwise.
Of course you do have to either have them trimmed regularly and by someone who knows how to do barefoot trimming (it's not the same trim that you get from a farrier who puts on shoes), but there are trained barefoot trimmers out there. Or ride them a LOT to keep the hoof worn from use. I use to ride my on the hwy some. Back in the 70's and part of the 80's my horses seldom needed much of a trim, because they were ridden almost every day and for extended periods of time. I was either working with the cattle or taking a long ride for a day or two (30 miles a day was a pleasant days ride).
At didn't realize it at the time, but in the early 70's a man (Gordon Nesbitt?...not sure about spelling the last name) rode from southern Africa to to central Europe on unshod horses. If you can find his comments on that trip they are pretty interesting. He wasn't a barefoot rider before that and took a load of heat from much of the "shoe the horse crowd" over going ahead with the trip on barefoot horses. Sometimes wonder what excuses they gave for his success after his barefoot horses completed that thousands of miles trip.
But I digress. With regards to your question. I will say go barefoot, but if the horse has spent years wearing shoes, then there may be some things that might be needed help the horse make the transition and can take time. I'm still dealing with one issue from my filling being shod, but I know in time she'll have feet as good as my mare's (three almost are now). It's a bit like the old Chinese tradition of binding a girls feet. After years of that if you suddenly you stopped binding them they wouldn't be able to walk for awhile. It would be terribly painful, (fresh blood flow and feet allowed to expand normally when stood on....yes an unshod hoof too expands as the horse walks) but with time and work their feet should return to normal and would be healthier than they were when bound. There should be loads of information about it out there.
Grabbed a couple of sites off google about going from shod to barefoot. Haven't read them, so I can't say if there of any help, but you can keep looking. I just grabbed the first two. Untitled Document Making the Transition from Shod to Barefoot
There is a German lady here in SC who was part of the old "Shoe the horse" school, but today is a wealth of knowledge about horses going barefoot. Her first name is Claudia, but I don't remember her last name. She use to do (and probably still does) a free online series of classes that you can sign up for. Extremely informative if you want to learn about the equine foot (stucture, growth, problems, treatment, etc.....)