No, whether there has to be a Big Rip is an open question. It depends on the equation of state.

The rate of expansion *is* _increasing_ over time. This is not an open question anymore. Nobel Prize in Physics 2011 awarded to Adam Riess, Brian Schmidt, and Saul Perlmutter: https://www.nobelprize.org/prizes/physics/2011/summary/

The Big Bang is NOT an explosion, but a metric *expansion* of space (the expanding dough or foam analogy is appropriate) so any discussion of matter density (mostly vacuum or not?) in that regard leads astray.

I disagree with your part about “matter”. The current explanation for the CMB is that when it was produced ca. 380'000 years after the Big Bang event, our universe had cooled enough (to ca. 3000 K) for matter as we know it to exist: quarks and gluons had already combined to protons, and protons and electrons had…

The Big Bang process is not an explosion, but (we think) a metric expansion of space: distances grow larger proportionally. So *geometrically* it is surprising that this expansion would not be isotropic and homogeneous.

I have been using Signal on Android since quite a while. Signal *encryption* of phone calls and instant messaging only works if the person you communicate with is also using Signal (or compatible client software; presumably WhatsApp, too, as they are using the same protocol now).