I mean think about it, we have seen the Spike plushy a lot in the series and realistically, out of all of Twilight's friends (Sans Discord and the other alicorns) Spike is the only one who could still be alive in this era. As we know, dragons live thousands of years and tend to sleep for long centuries. Plus it would just be cool to see Spike be sorta a wise figure for the Mane 5. There is so much potential for him.