The protocol certainly is not same and not exactly backward compatible. 1000-Base-T is fairly complex interface that is more similar to S(H)DSL than to traditional ethernet over TP or even anything that would any sane person call "baseband interface". By the way this is the reason that SFP/GBIC to 1000-Base-T transceivers are not supported by all devices with relevant slot, are not exactly compatible between manufacturers and sometimes are not compatible with non-gigabit devices on other end of the link (ie. not backward-compatible on the RJ45 side of things).
And before than in the days of first fast ethernet implementations there also were incompatibilities of similar type, which is mostly the reason that every managed or even "smart" switch allows you to disable auto negotiation quite prominently in it's configuration interface. Although that was more about software issues than about interoperable implementation being non-practical as is to some extent the case with copper SFP modules.
Bottom line: "I don't know what the next network interface will look like, but it will be called Ethernet and use RJ45 connectors on CatN (for some value of N) twisted pair ..."
And before than in the days of first fast ethernet implementations there also were incompatibilities of similar type, which is mostly the reason that every managed or even "smart" switch allows you to disable auto negotiation quite prominently in it's configuration interface. Although that was more about software issues than about interoperable implementation being non-practical as is to some extent the case with copper SFP modules.
Bottom line: "I don't know what the next network interface will look like, but it will be called Ethernet and use RJ45 connectors on CatN (for some value of N) twisted pair ..."