I think it'll happen again in the next 10 years regardless of if Liverpool do it this year.
The points levels of both City and Liverpool over the last five years is that insane its turned the league into a SPL - 2 dominant teams, everyone else just making up the numbers. Competition is no where near the level of was in 1999, where more teams could beat each other.
Same in Europe as well. English teams are getting to European finals or winning the CL on almost a yearly basis. There's just no great European teams about anymore, Bayern/Real at a stretch but Barca, Juventus, Ajax, Milan - none are at that level anymore. English football is the dominant force in Europe.
Just takes one of those top 2 clubs to have a poor season and the other will hoover up.