Worth noting that Finnair have now launched a very similar scheme: https://www.finnairshop.com/en/subscribe-to-avios

The prices are broadly the same as BA's subscription, so a useful option if you want more than 200k Avios a year.

Of course it's priced in EUR so not much good if you want to hit Amex spend targets (unless happy to take the 3% FX fee hit). Could still be useful for Barclaycard spend targets if you have the paid version of Curve like I do.