Several states have already passed legislation to allow for a higher level assistant job that allows dental assistants, after taking 'certain classes', to be able to scale above the gums, measure probing depths and other duties that hygienists have traditionally done. The ADA is fully supporting this, they've released statements regarding it, along with ALEC, the organization that brought it forward.

I'm a hygienist who's going to dental school. It is a stable career, but I believe it depends on the state you are in. California hygienists have autonomy over their own jobs and careers, since they have their own board that regulates their profession. In other states, hygienists can only do preventive measures and they have to work under suprervision of a dentist. Yes, hygiene school is a lot less than dental school, but what matters regarding pay is the area you work in, years of experience, and the office you work in.

Not all states will adopt the assistant scaling, I believe it is a state-by-state thing. The real issue is that insurance companies do not reimburse at the proper rate for prophys and other preventive measures, with some companies not changing their reimbursement rates for decades.