Isn't the answer in your own hands?
First step, ask yourself what fruit do you like? Apples, apricots, plums, peaches, pears, mulberry? Second step, research which fruits can be grown on a rootstock that is amenable to pruning and growing as a step over. Lots of fruits can be pruned to attractive shapes, but a step over is a very restricted shape. This may be the key issue.
For example one of the most dwarfing root stock for a peaches and apricots is VVA, but it will produce a mature tree about 8 feet tall. Could this be grown successfully as a step over? Well I do not know but I suspect it would be difficult, and I also suspect the yield may also be very restricted.
But hey, you will never know until you try! Why not simply go for it!