Change:
determine whether an immediate or delayed acknowledgement should be generated after processing incoming packets. <del> Acknowledgements of packets carrying CRYPTO frames SHOULD be minimally delayed, to complete the handshake with minimal latency. Delaying them by a small amount, such as the local timer granularity, allows the endpoint to bundle any data sent in response with the ACK frame.  ACK frames SHOULD be sent immediately when the crypto stack indicates all data for that packet number space has been received. </del> Packets containing PADDING frames are considered to be in flight for congestion control purposes QUIC-RECOVERY.  Sending only PADDING frames might cause the sender to become limited by the congestion <del> controller (as described in QUIC-RECOVERY) with no acknowledgments forthcoming from the receiver.  Therefore, a sender SHOULD ensure that other frames are sent in addition to PADDING frames to elicit acknowledgments from the receiver. </del> <ins> controller with no acknowledgments forthcoming from the receiver. Therefore, a sender SHOULD ensure that other frames are sent in addition to PADDING frames to elicit acknowledgments from the receiver. </ins> An endpoint that is only sending ACK frames will not receive acknowledgments from its peer unless those acknowledgements are

Discussion:
The editors assumed this was true, but I think it's worth stating this as a MUST to ensure clarity.
I'm a bit worried this misses the point. Ack-eliciting packets should be acknowledged yes, but so should non-ack-eliciting packets. By stating that ack-eliciting packets should be ACK'ed at least once, it is implied that this is not the case for other packets. This may be correct but not necessarily clear. For example for long transmissions where the peer does nothing but sending ACKs, not all of those ACKs will necessarily have to be ACK'ed. But what is the guiding principle for that? And, since you in this case are sending lots of ACK eliciting packets, you can easily ACK all the peers ACK's. So when would you not want to do that? A special case that could deadlock - e.g. too many ACKs to fit in a packet?
Also, when ACKs packets don't fit in packets, this would also hold for ACK'ing ack-eliciting packets. So you could end up having to not ACK'ing some packets and induce loss. Requiring an ACK for all packets would be problematic. I'm not sure we want that. The result could be very hard to implement while the practical benefit would be small: sending multiple ACK packets with different content due to overflow.
I just synced to master and now this seems to be an editorial change, at least to me. That being said, PTAL at the text and tell me if there are any other changes I should make.
It appears that the spec doesn't actually require sending ACKs for every ACK-eliciting packet. This could lead to a perverse implementation just not ACKing things with obvious problems.
Discussed in Cupertino. Add normative language to prescribe what should be ACKed. Reclassifying as Editorial (adds normative language, but we have consensus on that).
Generally looks good, but I don't think we can have an absolute requirement that every ack-eliciting packet is acknowledged.