This is not a new idea. Every decade or so, someone gets gung-ho about 12/12 from seed. But the fact of the matter is that cannabis will not flower until it is sexually mature, regardless of the light. So, what you are ultimately doing is depriving them of light during the time that they should be vegging and putting on bud sites. Some people will put as many as 4 to 6 tiny plants per sq ft. and as St. Nick mentioned, virtually all states have plant count limits where things start to get ugly. When I lived in Idaho, anything over 25 plants was a mandatory jail sentence. Each plant requires individual care, so taking care of 40 or 50 small plants is way harder than taking care of 4-6 large ones. Plants grown 12/12 from seed will often produce 1/8 to 1/4 ounce. You can run clones like this because they are the same biologic age as the plant it came from, however you will still experience small yields and the risk of jail from too many plants.
Most people who want plants to grow fast like this run autoflowering strains.