I think it is not that much difficult given how Guardiola has managed City ever since he took over as manager. He has made then PL champions 5 times out of 7 seasons and that really shows the kind of spectacular record Guardiola hold rights now. I think in 8-9 seasons he can make them equal to United if things goes like this. City are in control in whichever way you see and despite United and Newcastle improving, I don't see them getting dominant the way City are right now. I would say its very much achievable if Guardiola says for long term.
I think Manchester City could perform as good as they did in the just concluded season and perhaps, go ahead to win the premier league title again next season. Pep has really done a lot to change the fortunes of the club and I believe that if he remains with the club, he could go ahead to win more premier league trophies as well as other trophies.
Thanks to Pep, I see Manchester City as a disciplined club that would remain dominant in their games come next season. I know It’s a bit still early to tell but Manchester City has a really good chance of retaining their title again next season.