A max contract to Kanter won't hurt too bad since the cap is rising. It wouldn't be a smart move IMO, but it wouldn't be a franchise destroyer like a Joe Johnson veteran max contract.
If they max him they will be at 91M/year salaries. The year after, the salary cap will be ~90M and they would need to pay Durant. The 35% max for him would be ~31.5M, or 10 more million than they are paying him right now. At that time they can get rid off Waiters, Lamb and Perry Jones(around 10M), unless they decide to extend some of them(I really hope they give 8 figures to Waiters). They also would need to extend Morrow(I think he will command 8 figures for sure) and DJ Augustin. In general I expect them to be at about 100-110M salaries at that point(depending on what they do with the players on rookie contracts... The real fun though begins the year after... Westbrook and Ibaka up for extensions. Westbrook will be eligible for ~35M contract(20M more than he's getting now), same as Ibaka... To me it looks very possible that every single year they will be deep into the tax if they want to keep their current core.