What do I think? As interested in astrobiology I think the obvious existence of silent pathways makes the Fermi question "where are they" too unconstrained by false negatives to be "a big question". The "big question" here then remains the age old "are we alone".

A silent pathway would be the natural expansion out of a planetary system to the Oort cloud. It is the largest step on the exponential scale of technological and material resources. But it has also the needed material for transportable biospheres without the associated cost and risk of descending deep gravitational wells.

As for the astrobiology here:

1. Selection bias.

That is asked from a position of selection bias, we _are_ the first if we want to outdefine other intelligences we have observed.

More pertinent, biologists use to estimate that language capable intelligence may be as rare a trait as the elephant's trunk. On the other hand they have also come up with estimates based on diversity, which is more or less recovered after mass extinctions. Hence we have independent observable "worlds", and 1 out of 4 (3 large extinctions with land animals) made us.

All galaxies got started after reionization, so the parts of MW is about 13.5 billion years old. The first habitable planets aggregated shortly after the first star generation, the oldest known exoplanet is ~ 13 billion years old. We can expect the first life is about as old.

Then it takes billions of years to oxygenate a biosphere, which is a prerequisite for complex multicellular life. In our case ~ 2 billion years, but we can see that the oceans were still largely uninhabitable until cyanobacteria also regulated a nitrogen cycle. (Which put a stop to anoxic sulfur conditions.)

However, it is believed that the ocean of Europa has been supplied with large amounts of oxygen some hundred of million years after the ice cover formed. This seems to be a generic mechanism for the tidal habitable zone of gas giants. And the biospheres of ice moons are easily 10s of times larger than terrestrial oceans. So early intelligent life is most likely found there.

2. Life span of species.

Typical lifetime of mammal species is ~ 1 million years, and Homo seems to lie there.

5. Biospheres.

There are two viable cosmological economies, given the distances and the universal speed limit:

Information barter and colonization. As I showed above, Oort cloud colonization is likely and means silent dispersal. In any case, colonization means dispersal: population genetics shows that you need one crossbreeding/generation to keep a population from speciation. (Regardless of the size of the population, funnily enough.)

[Wormholes break general relativity with their closed timelike curves, so they can't exist - or the universe would have exploded.

Alcubierre is a viable GR solution but can't be used. If such a solution is created going FTL there is no way to put mass there to go FTL, since we can't break the universal speed limit for massive particles in the first place.]