First since this keeps being repeated, I'll keep clarifying it...
Swatch has not cut off any independent repair shops with the new policy. They have cut off 3rd party resellers of parts, so the only people who can't get parts are those who never bought them directly from Swatch in the first place.
If a watchmaker wants to become an approved shop there is a path to do so, so parts are still available to those who have gone through or will go through that process.
On the subject of the 20 year rule, yes Swatch states that as of the date of the last sale of the model from the factory, they guarantee that parts will be available for that model for a minimum of 20 years. They also state that if for some reason it is not possible to adhere to this guarantee, they will propose alternative offers that are fair to the customer - not sure what this means but my guess would be it will depend on the specifics of the situation.
Having said all that, Swatch states that they will stock parts for movements and other parts of the watch as long as possible, so beyond the 20 year time frame. It's clear that they already do this since I can still buy parts from them for movements that have not been made in 60 years or more. But the older the movement, the less likely all parts will be available for it. So just to give some examples the old 30 mm manual wind movements don't have all parts available, but as you move forward to say the 330 series autos there are a few more, but still not many. The 500 series autos have a few more parts available, and it's only at the 55X, 56X, and 75X series where pretty much all movement parts are in stock and available to purchase.
Case parts tend to run out sooner than movement parts do in my experience, and case parts is where Swatch indicates that in order to supply parts for repairs beyond the 20 year time frame, they will substitute parts that are technically functional, but might not be truly original to the watch.
Hope this helps.
Cheers, Al
