But it is the only chance we have ever had to directly view a largeish piece of another solar system, just millions of miles away. The next time probably won't come until we send a probe to Proxima Centauri.

While this is the only one we've seen so far, the current belief is that similar objects might actually quite common. A parallel newspaper article in the Guardian [1] cites a paper out of UCLA [2], and works through the math:

  The other group of astronomers, led by David Jewitt,
  University of California Los Angeles, estimated how 
  many other interstellar visitors like it there might
  be in our solar system.

  Surprisingly, they calculate that another 10,000 could
  be closer to the Sun than the eighth planet, Neptune,
  which lies 30 times further from the Sun than the Earth.
  Yet these are currently undetected.

  Each of these interstellar interlopers would be just
  passing through. They are travelling too fast to be
  captured by the gravity of the Sun. Yet it still takes
  them about a decade to cross our solar system and
  disappear back into interstellar space.

  If this estimate is correct, then roughly 1,000 enter
  and another 1,000 leave every year – which means that
  roughly three arrive and three leave every day.

So now that we now to look for them, it may be possible that we'll be able to find others, at least before the probe reports back from Proxima Centauri.

[1] https://www.theguardian.com/science/across-the-universe/2017...

[2] http://www2.ess.ucla.edu/~jewitt/papers/2017/JLR17.pdf