Musk is talking about the OSI layer 1 and layer 2 of the satellite network, which by definition needs to be something unique and custom. Nobody has ever built a LEO dual-satellite-CPE make-before-break architecture before. The closest thing is the o3b architecture which is intended for very large, costly customer terminals. This will still speak ipv4 and ipv6 just fine.
To gain a better understanding of why this needs to be totally unique/custom/proprietary, it is helpful to first have a thorough understanding of current high capacity dedicated geostationary orbit based systems (1:1 SCPC/MCPC with dedicated kHz) and various shared-bandwidth VSAT type systems (TDMA timesliced architecture between one large earth station, one piece of satellite transponder kHz, and a number of N fixed CPE terminals within the satellite's spot beam.
After understanding current geostationary architectures, dig into the "How" and "why" o3b was created and has been such a success, and its general system architecture which is proprietary.
Satellite engineer here:
The OSI layer 1/2 needs to be totally custom because we're dealing with a unique architecture of, just off the top of my head:
a) dual satellite LEO architecture
b) possible satellite-to-earth station trunk links, and satellite-to-satellite
c) CPE terminals that have no moving parts and use phased array antenna systems to talk to two satellites at the same time. From the stationary point of view of a rooftop CPE, the satellite that is currently "rising" from the horizon and will be soon overhead, and the satellite that is currently overhead and will soon pass out of sight.
d) Densely packed high frequency spot beams on a moving LEO satellite. The closest thing that's ever been built to this before is again the o3b satellites, but there are a great deal fewer of them, they orbit much higher, and have much larger spot beams than these small LEO high-Ka/V-band satellites will have.
e) Custom indoor modem RF tech to talk to the rooftop CPE and provide a standard 100/1000 copper ethernet handoff (and possibly integrated 802.11ac dual band wifi). TDMA timeslicing per CPE and bandwidth allocation - there is no way that an individual CPE will get 1:1 dedicated bandwidth 24x7x365, the amount of capacity in an individual spot beam sized area will be oversold based on standard network architecture principles that most people don't try to max out the capacity of their circuit 24x7.