One day someone might come up with one where you can gradually adjust the bust section southward
They already have! I am so lucky to have been bought one, by my lovely hubby, for my 'big' birthday last year, but they are ridiculously expensive. It's called Adjust-a-Bust from Morplan and they've been around for about 30 years, as my mum had one when she was in business. Unfortunately it was lost in a fire and I've hankered after one ever since.
As well as the bust going up and down, it also goes in and out. With a twist of the handle on the top, it can be altered from a size 8 to size 20 (dressmaking sizes, not rtw). She needs a bit of padding around the bust when she's in large mode but a bit of wadding does the trick. She also has 1 detachable arm and a removable 'mummy tummy'. She's invaluable for my alterations business, saving lots of time on manual size adjustments when I swap between garments of different sizes. She also likes posing for photos, although usually fully clothed
Suzie
https://m.imgur.com/a/X4Y5R