I don't really consider the bar to be set that high by the 24-105. It is very good for a 4xZoom, but it is also a pretty old design that doesn't hold up well against newer designs. Even the old Tamron 28-75 is as arguably as good or better at all shared focal lengths. It is hard to imagine this new Tamron lens would be optically worse than the 28-75.
That being said, real-world testing is called for. But I have no doubt it will do well as long as it doesn't have any production issues like Tamron has had on occasion in the past.
I have a hard time taking this post seriously. 'An old design'? I can think of a dozen lenses designed in the 1970s and 1980s that blow away most of what is made today. And comparing the 28-75 to any L lens, especially the 24-105 is laughable. This is probably going to bring out the 28-75 fans again but I don't like that lens and the variance in copies is extreme.