The part that is required for dapp compatibility is that other contracts can call into the Safe with EIP-1271 support. This implementation is handled via the FallbackHandler functionality. This is very flexible as you can change it without having to upgrade the core contract.
The change proposed here is that the Safe calls into other contracts using the legacy EIP-1271 specification to support contract signatures for owner addresses that are contracts.
As it is not using the latest version of EIP-1271 the usability of this one can be challenged. There seems to be very little demand for this feature (as it is not compatible with other wallets, but noone is providing feedback on this) and it just opens up an alternative path which could be exploited if wrongly configured.