So US charter schools and UK academies / free schools are able to hire anyone they see fit as teachers, or as responsible adults in charge of young people. Some make much of this, claiming that this allows these schools to make "better" appointments and which should be extended to all schools.
Certainly, such an approach may allow for some agility or flexibility. It may also allow for specialist knowledge or recent experience, for example in technical fields. However it also begs the question: what is a teacher?
Teacher preparation programs have recently come under attack, some have been called effectively "useless". Yet, they do all fulfill one very important purpose, that of a filter. Not everyone should be in front of a class, be it due to temperament, personality, ability to pitch concepts at an appropriate level, willingness to meet the paperwork and compliance demands which come from being with other people's children.
They also allow schools, school leaders, co-teachers, mentors to provide some shaping experiences and advice, and even to counsel out some who should not be in a school.
I suspect there still remains a need for certification of some sort, but what it involves and where/how it is provided do of course require further discussion.