There's a 20+ page paper written about it, it's not exactly a secret Lol.
There's even an open API for stats that you can test it on (and an entire season worth of stats to use as a baseline, from when they placed you exactly at your MMR), so nothing is stopping anyone from reverse engineering the code.
But most people fall into the laymen category and aren't going to understand all that anyway, which is why they dumb it down to a more long-term average of CSR. That's why your MMR is hidden, because there's a lot that goes into it and nobody is going to take the time to understand it and instead, just complain about things they don't understand.
What really matters to the user at the end of the day is whether the rank is accurate, and CSR provides a more general picture of that to give feedback based on.
The impression I get from Dr Menke who created the system is that it's not possible to add stuff to the postgame matches in H5, but they're considering adding things in future games.This, and I also get the impression from Josh that if people knew it they might be able to boost easier and what not.
He seemed to note those concerns as more of a general "initial hesitation" at the beginning, or just "taking it slow" to see how it works in a blind setting (ie. as a control, and to make sure there's no serious bug that got overlooked).
But in fact, one of the main goals with Trueskill 2 was to make it resistant to manipulation by design
(eg. everything being based per-minute, everything as a relative comparison to other ranks, and CSR acting as a clamp) so that they wouldn't have to keep re-working it and dealing with manipulation tactics on a case-by-case basis.
So I really don't think the boost-ability aspect is a serious concern on a more long-term basis, more of an initial footnote for early testing. The true aim in regards to boosting is actually to remove the need for secrecy in the first place (eg. as Luke noted with their desire for more
information in upcoming titles).
In fact, you can see this in his posts -- he has given more & more details as time has went on, and by this point I'm sure anyone clever enough could figure out a basic framework for generating estimate MMR graphs like he has posted recently -- although there wouldn't be much point because, as the system continues to prove its resistance to manipulation, it becomes more & more likely that those graphs will just become the standard anyway.