I haven't yet seen a mini, foal or adult, that paces, but several years ago I heard that there were some in a couple of herds years ago.
When we had Morgans we had a couple that would singlefoot; we had one foal that would do the most amazing running walk (huge stride under with his hind feet, nodding head, the whole bit! Would have made a natural big lick horse if he kept it up) when he was a young foal. (Same breeding as the two that did a singlefoot) He outgrew it and by the time he was a year old never did it again. I'm not sure if pacing is likely to be outgrown, or if your foal will do it all his life.
To add to this--a fellow in this area had two mares that were bred similar to our singlefooting mares, and his mares paced. He would try to show them in dressage and it didn't go well at all because the mares would change from trot to pace to trot again as they pleased. The one mare as I recall would pace more often than not. The other one would trot for awhile and then change to a pace & then would stay at the pace for awhile--it had to be extremely frustrating for him and after a year or two he sold them and started showing other horses--ones that didn't pace.
I was always thankful that our mares did not pace--the singlefoot was nice to ride, and it never interfered with their true trot. Both of our mares were good trotters and they would never break gait--we would cue for a singlefoot, but if there was no cue they would hold the trot. There was no problem in showing them.