My main problem with offering Wall the designated 5 year max now (25% of a team's cap space), is that we pay star money for a player who, at the moment, isn't a star.
He has everything to become one and reportedly he's doing all the right things to maximise his potential but right now, he is not a star level player. And we don't have to extend him now! Nor do we need to before october 1st. He has a full year left on his rookie deal.
So, what happens if we don't extend Wall's contract right now? Well, he'll be a restricted FA next summer, just like Seraphin and Booker who are eligible for extensions now as well. And what does restricted Free Agency actually mean? It means that any team can make Wall an offer up to the 4 year max and we can match any offer he gets. If Wall does make a leap to stardom this season and therefore we are certain the money is well spend, then by all means: pay the man. Make him our designated player with a 5 year max. If he stays the very decent point guard he is now with an occasional hot streak, than let him become a restricted FA. Some team will offer him the 4 year max and we'll match. If no team even bothers because they know we'll match, then offer him a Curry/Holliday-like contract. By doing this we'll still have the 5 year designated max for our Durant to Wall's Westbrook (although technically Westbrook is a 1B player and not a #2).
Some are afraid that Wall might be pissed. Well,so what. This is a business and the simple fact is, Wall is hasn't shown he is a star caliber player yet, so don't pay him as if he did. There is time for him to prove it and if he does, then he'll get payed. Besides, if we start winning more (either because Wall is a superstar and makes the super max or because Wall is not a superstar and makes the 4year mini max/is appropriately paid a la Curry/Holliday and therefore the super max is paid to a superstar) Wall will turnaround during his contract, unless he signs and demands a trade immediately. That's a risk I'm willing to take, especially since very good point guards are not as rare as very good bigs and forwards.
I'll end with Wall's own words as quoted by Michael Lee in an article concerning his impending max deal:
nothing was ever given to me. I always earned it, so I'm willing to do that