Worst that there are also unknown Virus and Bacteria found in the Permafrost, which are also defrosted with the Climate change. A lot are also still life..
Not less evolved. Just evolved differently for alternative environmental circumstances.
There is no hierarchy of evolutionary traits. Just an amalgamation of traits that are or are not useful in the current environment. What genetic makeup is effective in one place and time is useless in another, and what was once useless may now be beneficial.
We have no clue how threatening they could potentially be.
They are investigating it, some million years in the oldest beeings in Earth don't make evolutive difference to the current ones. The only question is, if they can infect humans or animals or not.
The climate change make that all tipe of indesirable things are defrosted, adding more dangerous diseases to the existing ones.
Viruses and bacteria don't evolve to kill you. They propogate in your system to spread themselves. It's actually in their best interest to keep you alive, so the more evolved ones would be less deadly because they've had more time to dial it in. Not that evolution is something they choose, it's from mutations that work more or less better.
I love that "Uh, guys?" is a real in-character reaction and moment in many episodes of SG1. This story easily could have been a plot in the show.
While Star Trek had these wonderful "this is why we explore the galaxy" moments, SG1 wasn't afraid to place characters face-to-face with something or someone that would just erase existence or end humanity if the next moment wasn't handled the right way.
A lot of times memes are what they are because they're harder to fact check (can't copy and paste text from them). People use them to spread misinformation for fun. -This is actually a confirmed meme though.
Except for a couple of details from the link you posted: there were only two worms, and they are likely of the same age (don't think this can be determined more specifically than 'around 40 thousand years'), and the picture is absolutely wrong.
Are we just looking for imaginative ways to destroy ourselves at this point? We have enough options already! But we have to keep looking for more creative previously unknown ways to kill ourselves.
Xeno-archaeologist 1,000 years from now: ..... yeah .... it's another one .... fourth one in this sector .... just blew themselves up and destroyed everything for some dumb reason ... probably economics like in that last system 35 light years away .... too bad ... if we had arrived earlier, we could have helped them out ... oh well