MagSafe for accessories
So, there are two types of MagSafe accessories: MagSafe chargers and then MagSafe-enabled cases, wallets, mounts, etc.
Apple has already announced it is integrating MagSafe into proprietary chargers as well as the back of its own silicone and leather cases, which will allow you to use MagSafe chargers even while your device is in the case. Third-party accessory manufacturers will also be able to adopt MagSafe technology into their own products, opening up the door to all-new accessories.
Do MagSafe accessories exist yet?
Yes. Apple has launched a few MagSafe accessories.
MagSafe chargers
Apple has announced a MagSafe Wireless Charger for iPhone and a MagSafe Duo Wireless Charger for iPhone and Apple Watch, although the latter isn't available yet.
Finally, Apple has created its own leather wallet that easily snaps to the back of the iPhone 12 or a MagSafe-enabled case. Leather shell cases from Apple are also in the works. In other words, expect all future accessories from Apple to be MagSafe-enabled.