The title does not match the fact in the article.
The coexistence in question is (or was) between radical Muslim in Tatarstan and the traditionally (*) quite docile Tartars; in other words, the subject of the article is the ethno-religious politics of a relatively small region inside Russia.
This docility is apparently coming to an end due to the influx of more radical Muslims from, for example, Chechnya.
Tatarstan was a model of peaceful coexistence also in the sense that the relationships between Russia proper, Christian Orthodox overwhelmingly, and Tatarstan, overwhelmingly Muslim, were indeed harmonious. But unlike in North Caucasus, the tension is between two kinds of Muslims, not, so far, between the ethnic Russians and the ethnic Tartars.
However, none of that can be projected to a wider theater of relations between Russia proper (i.e. culturally Orthodox ethnic Russians) and various Muslim lands in the Russian Federation. There, the picture varies region to region: two brutal wars in Chechnya, tense but not violent anymore rest of North Caucasus, peaceful Tatarstan and Bashkorstan.
Of course, Russia lost her satellite formerly Soviet republics, that are now independent.
Tartars are remnants of Great Mogols hordes who invaded and dominated Russia for a few centuries. At the end Russians subverted their culture and government structure making them kind a vulnerable and then militarily destroyed their urban centers. It become possible as soon as Russians fond a way to corrupt some of their aristocracy and Russians also had a firearm technology while Tartars still relied on bows. A lot of people initially welcomed Russian subversion as their lifestyles seemed to be an improvement over their spartan military-style islamist regime. By mid 16th century all the remaining Mogol Khanates were incorporated into Russia and their leadership were killed or forcefully baptized.
Tartars were calm for centuries but some closet revanchism emerged in earlier 1990s.
I think it is very important for Russians to contain it because Tartars are actually a huge minority just like African-Americans in US. They are present in every part of the country in huge numbers.