For example, if you are building to black/green, one of the key tools is a green sorcery to drop cards in your graveyard. Guess how many of those there are in Kaladesh/Aether Revolt? ZERO... that's just crazy and it's the reason why Standard has sucked so bad for the last two years minus a core set. Let's add Origins, just for kicks. Now we have Gather the Pack.
I think if you expand to M19 (which better have something like Gather the Pack in it, and then add all of Amonkhet/Hour of Devastation, you will then have the basic tools to build any one, two, three color commander deck. The latter two bring in Benefaction of Rhonas.
If you do Kaladesh/Amonkhet/M19, you will have a core set with a bunch of toolkit cards, and a large enough selection to go in many directions for commander builds. Also, all but M19 will be rotating soon, and that means you can bargain hunt some of the better cards you may not have pulled as they rotate out.
Finally, about commanders, KSH by itself is really lacking, and so is Amonkhet. But KSH + AMN isn't so bad, plus M19 is already coming with some sweet commanders even this early in the preview season:
White
Sram, Senior Edificer
Oketra the True <AMN>
Djeru, With Eyes Open <HOU> Tutors for a Planeswalker
Blue
Baral, Chief of Compliance
Kefnet the Mindful <AMN>
Padeem, Consul of Innovation
Unesh, Criosphinx Sovereign <HOU>
Black
Bontu the Glorified <AMN>
Gonti, Lord of Luxury
Razzaketh, the Foulblooded <HOU>
Yahenni, Undying Partisan
Red
Hazoret the Fervent <AMN>
Kari Zev, Skyship Raider
Neheb, the Eternal <HOU> Minotaur
Pia Nalaar
Green
Oviya Pashiri, Sage Lifecrafter
Rhonas the Indomitable <AMN>
Rishkar, Peema Renegade
Multicolored
White/Blue: Temmet, Vizier of Naktamun <AMN>
White/Black: Kambal, COnsul of Allocation
Blue/Black: The Scarab God <HOU>
Blue/Red: The Locust God <HOU>
Red/Black: Neheb, the Worthy <AMN> Minotaur and
The Scorpion God <HOU>
Black/Green: Hapatra, Vizier of Poisons <AMN>
Red/Green: Samut, Voice of Dissent <AMN>
White/Red: Depala, Pilot Exemplar
Blue/Green: Rashmi, Eternities Crafter
White/Green: Missing in Action, maybe from M19
Colorless:
Hope of Ghirapur
I may even decide to sprinkle some Dominaria into the mix, adding to taste.
