Re: "the same old type of business calling themselves Agile"
Oh, come on. When did certification ever solve - well, anything really? Are you trying to reinvent ISO9001?
Self certification is as good as its enforcement, which is to say, generally it takes complaints from suitably motivated agitators to make any improvement. How would you foster a climate in IT where whistleblowers are celebrated and welcomed by their next employer?
External certification means a whole framework of oversight board, advisors, auditors... Who would pay for all that, and why?
Basically, the big effect of either one is to favour the bigger established players who can put the appropriate effort into making sure the required boxes (and only those) are checked. Most startups and smaller players - including, most likely, the most genuinely exciting companies to work at - would be excluded because they've got more interesting things on their minds.