Increased human unemployment might, actually. If both cost and time weren't huge barriers, I expect more people would ride.
But I think the future for humans looks somewhat similar to that of horses today; a small number of us will still be "working", but more because of individual preferences than any kind of need.
It's not about cost and time; horse maintenance is more labour intensive, and then there's a problem of waste. Actually shortly before the first automobile was constructed, London authorities were worried that if the demand for horses keeps increasing, the city will literally be drowned in manure.
But I think the future for humans looks somewhat similar to that of horses today; a small number of us will still be "working", but more because of individual preferences than any kind of need.