Only 14 head coaches have two or more NBA Championship titles, and another 21 head coaches have won the NBA Finals only once. Kerr is currently the fastest head coach to win two rings or more in a short period of time.
Kerr is relatively young and he can keep working as a head coach for the next 10 years and Curry is likely to play until he is 40 and that gives Kerr enough time to win more rings.
Is Steve Kerr the NBA head coach with most championship rings?
No, the head coach with the most rings is Phil Jackson with 11 NBA Championship rings (1991–1993, 1996–1998, 2000–2002, 2009, 2010) including a back-to-back title just like Kerr. But there is another head coach with 16 rings (coaching and executive career combine), his name is Red Auerbach, he won 9 coaching rings and another 7 as executive during the 20th century.
Kerr has enough time to get past Phil Jackson, he will need to win eight rings which is a long way but not impossible as long as he has a similar class of players as he has today with Curry, Thompson.