That's not how it happened at all, this is completely backwards.

People moved to the cities not to escape farm work, but because mechanization in the forms of tractors etc made them redundant... far less people required to work the same acreage and more people needed in cities to work the factories.

I would think the next phase is overall more efficient land use in the form of smaller factories and even more productive acreage (mechanized greenhouses etc)

This would make way for more ornamental gardens and open space in and around cities... so not people migrating but suburbs becoming more rural and cities becoming more suburban. Autonomous vehicles, e-bikes etc, would also eliminate traffic and restore asphalt into greenways.