The sticking points I have with the venus-life hypothesis is in order to survive the 80% sulphuric acid clouds, either:
1) the life forms have a completely different basis to Earth (e.g a non-carbon base). That would be an even more shocking discovery.
2) they have an incredibly tough sealed acid-resistant exterior, like kevlar but stronger. In which case, how do they get nutrients in etc.
3) They don't even attempt to survive in the clouds of acid gas, but in some other environmental niche.
If we were observing Earth from Venus we'd be completely unaware of environmental niches that can only be observed from relatively close. From odd micro-environments like black smokers to the whole range of macro-environments that range from tropical rain forest, tundra, permafrost, cold deserts, hot deserts, cave environments and so on. Drawing a broad conclusion from the first environment that can be observed through a telescope with a spectrometer would be short-sighted.
Well, the niche the researchers propose is in the clouds 40 km up. There are Hadley cells that circulate a permanent cloud layer, where the clouds are mostly droplets of sulphuric acid. It is possible that the phospine is produced somewhere else and migrates to the cloud layer.
Also, one has to make allowance for billions of years of evolutionary pressures operating to produce viable organisms. We have bacteria that have evolved on Earth to thrive in the cyanide loaded tailings of gold mining, and in the pH 0 tailings of iron mining, all in the very short period of time, in evolutionary terms, that those processes have been in use - both environments which one would naïvely say were inimical to life as we know it. Also, what's to say that this is ancient life, if indeed it is life, that we're now observing? What's not to say that this is the relatively recent beginnings of life in that environment?
Sure that is true. We are basing all our expections of extraterrestrial life, and detection methods thereof, on extrapolations of Earthly life. It could be that life is common, but carbon based life using water as a solvent is just one of many types. Maybe evolution on Earth has not had to try very hard, because most of Earth is quite benign. That may be because life adapts the planet to it's preference - the Gaia principle. However, if Gaia thoery is true, as a corollary of that, we might think that if life on Venus had started when it was benign, them it should have maintained those benign conditions instead of runaway greenhouse effect.
There are so many questions about life and evolution we don't the answer to, it is far too premature to assume life is a cause of unexpected chemistry. Planetary geochemistry is also largely unknown, it is really too simplistic to say "if we find substance X, that means there is a good probability of life". I like the adage "the answer is never life, until it is proven to be life".
There is also an intriguing possibility there borderline life-like processes. Something between prions and viruses. Molecules that can use a catalyst to self-replicate. Logic by itself will not answer these questions. Only studying the environments in more detail will help.