They already demonstrated the E.Coli bacterium evolving the ability to metabolize citric acid... that makes it a new kid of bacterium (the inability of E.Coli to metabolize citric acid is one of its defining characteristics).
And the color white was a "defining characteristic" of swans until they found a black one.
And the black swan (Cygnus atratus) is, in fact, a separate species. So even by your own argument-by-analogy, you've agreed that the new bacteria should also be considered a new species, and thus evolution has been observed to occur.
Look, I believe in evolution, but never has there been found a parent species to something alive today.
My grandparents have all passed away, but I'm pretty sure I'm still related to my cousins.
In other words, scientists can not point at any two distinct species, living or extinct, plant or animal, and say that this species evolved directly from that one.
We've had plenty of genetic evidence from preserved material to say exactly that. But the big news about Lenski's experiment is that not only do we have living examples of a species which evolved directly from another species, and not only do we have living examples of that original species, but the scientists actually watched it happen.
Show me the fossils of the prehistoric rodent that evolved directly to today's rabbit or rat and the debate will end.
Rodent ancestors appear is the fossil record around the late Paleocene. We may not be 100% sure the actual individual fossils we have are direct ancestors of currently living rodents; they may be, say, great-great-...-great-uncle rather than great-great-...grandparent. But that doesn't matter since the existence of the latter is logically implied by the existence of the former. The debate, among anyone who actually knows what they are talking about, has been over for a very long time. The only ones claiming otherwise are the creationists.