Ahead of buying Kaladesh packs, I have cards from these sets ready for a fun deckbuilding cube: All of Scars of Mirrodin block, some core set cards-especially M12 and Origins, Shadows over Innistrad block, and Khans of Tarkir (only that set). I have some on paper, but mostly I will be having fun building these decks online.
Thraben Inspector is an all-star. It's a solid chump blocker, and you get a Clue token you can use to get one card drawn for two mana. That's a really good deal. In SOI Investigate is in Bant (White, Blue, Green). In a cube, that covers three colors.
Boros Elite is great in a White/Red aggro weenies build. Dutiful Thrull and Mardu Hateblade are good for White/Black builds.
Bloodsoaked Champion will work great in a Blue/Black, White/Black, or Esper (White/Blue/Black) Reanimator build.
Elves is the best tribal build of this cube when we combine the great elves in Origins with the ones in Kaladesh. Thrull Parasite is a keeper for a White/Black build.
Legion Loyalist and Monastery Swiftspear are great aggro cards in White/Red, and Red/Green.
Vampires are a fun build, and worth trying with a few artifacts from Kaladesh. These artifacts won't make the deck any better, but they can make it more fun, I guess?
In the right deck Cooperhorn Scout should be great. Permeating Mass is a great staller in Blue/Green and Black/Green.
Llanowar Elves belongs in any deck in this cube that is running Green. Glistener Elf is the starting creature for Infect if I have enough cards to build it. Memnite is great for an all-artifacts deck.
If Hex Parasite can be used to remove planeswalker loyalty, that is great. I am not sure I am correct and I need to try it. Signal Pest is a keeper.
I am not sure if I can build a good Infect deck out of a small selection of cards, yet in a small cube I should be able to pull it off.