Adding on to this, the Tempest Trial's Banner will most likely have M!Robin, Lucina, Nowi, and Tharja. Which is a very very very very lame banner considering we'll get Not!Lucina. "He'll" have the same stats but guaranteed neutral is better than maybe-sorta-OK.
Lucina being in the banner would be the worst. Cherche, Chrom, Cordelia, Frederick, Gaius, Henry, Lissa, Stahl, Sully, adult Tiki, and Virion would at least be units you can't get through the first Tempest Trial. Technically, everyone has a shot at getting a free Lucina even though she's in her alternate Marth form. Same stats, probably same skills or at least the same special Aether. It'd be hilarious if they surprise bomb us with some of the Awakening kids. Brady, Cynthia, Gerome, Kjelle, Laurent, Nah, Noire, and Yarne would all be good choices. Inigo, Owain, and Severa would all be sword units which we really don't need. Inigo and Owain at least get a pass since Inigo could be a dancer and Owain would be a different unit from Odin, a mage, and there's the whole Missiletainn could be his unique weapon. Severa would basically be Selena which could go literally if she has the same stats making her pretty pointless. Now, if they did a post-Future Past Severa, then maybe she could be a Pegasus Knight... Anyway...
As for the Vantage Banner, that's probably going alongside Tempest Trial's banner because Vantage is great for saving units from dying. So that's Rein, Lon'qu, and Gordin. That means pulling for blues is the best for this banner. Maybe if we're lucky we'll get a 4th Hero that's totally new. But why would they do thaaaaaat, hmmmm?
It'd mark the second time a banner had 3 units since the first Voting Gauntlet which had 2 banners with 3 units only. It would also mark the third time Reinhardt has been on a banner which would be the most any unit's been on and he'd tie with, assuming your guesses for the Tempest Trial banner is right, Lucina and M!Robin.
If the Vantage banner ends up being all new units, I'd laugh. There are several units in past games with Vantage.
- From Awakening: Say'ri and Yen'fay who would probably be GHB
- From Fates: Fuga,
Pickle Boy Hisame, and Sumeragi who should also probably be a GHB
- From Genealogy of the Holy War: Arden (Sword Knight), Ares (Cavalier and Mystletainn), Dalvin (Mercenary), Hannibal (Sword Knight), Iuchar (Axe Cavalier), and Lex (Axe Cavalier)
- From Tellius: Mia (Myrmidon and possible Wo Dao if they base her on RD) and Naesala (green? flyer)
- From Thracia 776: Halvan (Fighter), Machyua (Myrmidon who promotes to Hero instead of Swordmaster), and Perne ("Thief Fighter" with the King Sword, basically a personal Brave Sword)
They could just take four units from Genealogy to make a Vantage banner. Arden and Hannibal are probably the best picks considering we only have 1 summonable sword knight. Speaking of which, apparently Zephiel is the next GHB repeat. Hmm, don't know what I want to do with extra Zephiels... Life & Death and Wary Fighter are great, but I don't know who I have that I want to use them on, but I know for sure when it comes to units I don't have like both Cordelias, Hinoka, Olwen, etc. Er... Kagero, I guess? Maybe Gaius to make him into a bootleg Jaffar who doesn't have -Atk? I'd rather get Ursula other skills first before inherit L&D on her. Wary Fighter's not that useful when I only have Draug and Gwendolyn as my other knights. Garon when? Oh, and no Distant Counter, so a full armor team wouldn't be easy pickings for ranged units and no spare units for Pivot, so using knights with other units isn't as a much of a pain.