From the docs on GSN:
Third-party contracts you inherit from may not use these replacement functions, making them unsafe to use when mixed with
GSNRecipient.
This is of course related to the new _msgSender() and _msgData() which must be used in place of msg.sender and msg.data when accepting GSN meta transactions.
Does this mean that all Zeppelin contracts, upgradeable or not, cannot be inherited from anymore?
Not at all! We've of course thought of this 
and all OpenZeppelin contracts are now written in such a way that if GSNRecipient is present in the inheritance tree, they'll automatically start using the GSN _msgSender, with no extra overhead on non-GSN contracts.
This means however that you must use the contracts from the package: copy-pasted contracts from older versions will not work.
Fantastic!
Yeah the copy-paste might cause troubles for some tools. I remember I once had issues with contracts imported from node_modules. I think that was with MythX.
I think to clarify we mean contracts from openzeppelin contracts-ethereum-package correct? @nventuro https://github.com/OpenZeppelin/openzeppelin-contracts-ethereum-package
Both @openzeppelin/contracts and @openzeppelin/contracts-ethereum-package have GSN support, but ethereum-package is the one to use if you're using the SDK, yes.