FWIW some aikido orgs are more closed than open, some that were quite closed are now more open and vice versa over time.
This is very true and Aikikai Australia are certainly not the only organisation to have placed restrictions on their members training elsewhere. I doubt this is peculiar to Melbourne and Victoria but I think it is the main reason why there are so many splinter groups there. I personally know of at least 20 dojos that have been operating independently and successfully for many years, run by very experienced and dedicated teachers- many of them friends of mine.
Some people just like to be independent while others choose that option to escape a paranoid organisation or Dojo-cho. However, getting back to the Hombu recognition issue, there are several Dojos in Victoria that conduct their own gradings under the direct guidance of the Aikikai Hombu who are not affiliated with Aikikai Australia.
We did an estimate once based on independent dojo student numbers and figured there were as many people training in independent dojos in Victoria as there were in the affiliated organisations. That was a 10 years ago and I have since moved to another country so am a bit out of touch but it probably hasn't changed very much.