@TizerorFizz - well these days it is easier. You could easily sign your DC up to a DuoLingo trial and see if they like it? Then get them to practise a cross section of different languages from Mandarin, to German, to Russian, French etc.
I knew my DC would be good at languages because I did MML before doing Law. And their brains are like mine - very good memory, natural verbal reasoning and logic aptitude, great aural skills (better than mine because all do music to a high level). They could just do Latin as well. However, they are also good at Maths at the early stages up to A level (all of them). Those who were not perfect at non verbal then stagnate at a certain point in Maths.
The question is not just are they naturally good at it. The question is more are they going to be passionate about it and want to do it long term. Especially in this country, MML is not properly emphasised in the education system.
So if I were a parent passionate about MML and on the Victoria train line, yes I would do it if I had a bright child who is a keen reader, likes words etc and can spot patterns easily.
What I do not know is if most of those places end up going to bilingual children as they are more likely to have the natural aptitude, having been exposed from birth. The state schools won’t be allowed to test for acquired knowledge just like Wilsons cannot test based on those who have already passed their Grade 8 age 10. However, whether those bilingual kids and Grade 8s also have the natural aptitude - probably more likely. Especially on the music front because children tend to do what they are naturally good at.