TLS Session tikets invalidate Perfect Forward Security (PFS)
This looks like classical case in security: Solving problem A by moving it to B, with identical consequences and challenges.
It is obvious session tickets decryption keys must cached (long) term and shared between servers! In fine this means that some short of Master key (or its derivatives) must be kept long term.
Then master key (or derivatives) can be used then to decrypt old tickets, therefore breaking PFS benefits.
Unless more about the session tickets is disclosed Google cannot boast any real security benefit on this change!