That’s not how it works.

A hammer is not more obsolete for driving a nail because pneumatic nail guns exist.

Using just a hammer on a commercial framing job is silly, however, because pneumatic nail guns work better. Everyone still has a hammer ready though, because it is still needed.

Using a pneumatic nail gun to hang a picture is silly, because it is so overkill (and expensive) that it actively makes it harder to do the job.

This tech doesn’t obsolete existing fiber for last mile because the extra cost associated with producing and splicing it dwarfs any potential gains (which would likely be in the 10’s of ns).

If it is proven to work well, this may obsolete existing transoceanic/transcontinental fiber runs, where the latency difference will be noticeable enough the cost is worth it. However, it’s highly unlikely that anyone will actually turn down any of these existing lines. The different is not so much that the old lines are useless.

If, eventually, this new fiber is at the same price point and as easy to work with as the current fiber? then the current fiber will be obsolete.