Fact checking says that Tesla has "reliably liquid cooled thermal environment which helps a lot" and he says they are drop-in replacements on the S, X and 3.
Seems that Mongo is saying that the present S and X do not have liquid cooling at the board even though the 3 does. I don't know about the S and X but I do think the board is the same among the present S, X and 3 so whatever today's board requires seems like the new NN chip set should support.
I would like to have confirmation that the S and X do not have liquid cooling in the present board and if that is correct then the term "drop-in" may be overly optimistic for the S and X.... unless the liquid cooling is not required or there can be some other clock speed adjustment that tempers the need for liquid cooling or something else (ie a fan).
To expand on this a bit. It is my expectation that every new design will have a better future model to build toward. Each new design builds on assumptions and they are better in every iteration. S & X may be able to fully support this new NN board but if it becomes 4 NN chips then that probably won't be supported.... probably not even the present 3 but perhaps in the Y (it's a newer design with a better set of assumptions).
High level of interest in this one, since I have an MS built in Feb 2018 and paid for FSD. Since then have heard repeated promises that this will give me HW3 upgrade, will ge quite disappointed if this turns out to be not true.