I think you'll see the SAMD21 variant boards like the Arduino Zero, around in some guise or other in the near future.
Arduino has invested a lot of time and effort in creating and maintaining the SAMD21 core code and you now see this investment being leveraged with the SAMD21 based, MKR series with their Internet of Things connectivity.
As for the future, it's difficult to say. Adafruit are currently creating a number of Arduino compatible SAMD51 (120MHz, ARM Cortex M4F) boards that are also based on SAMD21 core code. Whether these might perhaps spawn a new generation of faster more powerful boards? Time will tell.
In the strange world of electronics, in a market place where despite more capable offerings (such as the Arduino Due), the Arduino Uno remains their flagship product, the future, as well as the economic viability and longevity of each board is probably very difficult to predict.