Raff capashen gives the entire deck flash while having flash himself, making it very powerful, especially in this deck. Shalai, Voice of Plenty offers considerable protection, while Jhoira, Weatherlight Captain serves as a draw engine and removal magnet. Lyra Dawnbringer is a powerful late-game threat that cannot be ignored under any circumstance. Teferi, Hero of Dominaria is, well... Teferi. Meanwhile, on the lower end of the curve, we have Senate Guildmage, with her looting effect that is massively helpful in enhancing the quality of our draws, and Captain Lannery Storm and her treasure-based ramping (that sometimes enables Shalai's ability!). 

We run Urza's Ruinous Blast to really capitalize on the historic aspect of this deck. It's essentially a Cleansing Nova with both effects chosen, except it does not hit most of your cards. And if you have a Raff on the field, it's an instant! It's just crazy value, really. 

Sideboard offers a player a number of solutions to keep other meta decks in check. This is the most difficult part currently, as the meta is still somewhat in flux, but I'll do my best. :)

Against golgari, sultai and drakes, we have Scrabbling Claws. It deals with undergrowth cards as well as both drake and phoenix by removing their resources while being a conditional instant itself if you have Raff on the field, and cycling itself if you don't have an use for it.

Sorcerous Spyglass is excellent at shutting down planeswalkers in a pinch. It can also turn off the transformed lands (Search for Azcanta // Azcanta, the Sunken Ruin, Legion's Landing // Adanto, the First Fort, Thaumatic Compass // Spires of Orazca and others). Being an artifact, and thus, historic, Raff can bring it at instant speed, letting you respond to a planeswalker and shutting it off before it even acts. Once it hits the field it also gives you information on your opponents' hand.

Maybeboard: Ral, Izzet Viceroy offers a strong package in draw selection (almost a surveil 2 -> draw 1), but his removal and ultimate wouldn't be of any use to us, seeing how the deck only runs 8 instant/sorceries in mainboard. Nonetheless, his presence is enough of a threat to shift focus from an opponent to him. Bonus points for being able to stay on board together with Teferi, giving you almost insurmountable card advantage. 

The Immortal Sun is a death sentence against control decks if it manages to stick on the field, giving you great card advantage and blocking their planeswalkers. And if you happen to have Raff (notice the theme? lol) it's even better, as you can catch them with their pants down, playing it in response to the PW, preventing even the first usage. That said, its cost is prohibitive at 6 CMC, which is why it was demoted to maybeboard.

Breeding Pool, Stomping Ground, Temple Garden - the green splash could benefit the deck, letting you use Shalai without depending on Lannery Storm, and allowing us to side in Rhythm of the Wild. Making our creatures uncounterable would help tremendously on the control matchup, and if we have shalai on the field, they're virtually immune to anything but board wipes (which sadly Esper runs lots of...)

General comments: RNA made plenty of new archetypes available, but sadly there are almost no cards that enhance this specific one. The deck was already relatively underwhelming in GRN, but now... geez. Sultai's presence is way too oppressive. 

History of Benalia is, unsurprisingly, amazingly powerful. However, its mana cost is also very intensive color-wise which, while improved by the release of Hallowed Grounds into standard, still meant it was often a dead in the early game. It's not a card meant for 3-color decks (duh).