Well, no Elspeth follower card in BotG, but there is still a chance in Journey to Nyx, as well as a chance for an Ajani one if Ajani has a card in that set like the promotional art seems to indicate. I'm speculating it will be a Green/White Ajani, to fill in that planeswalker color combo and have Ajani cover all of the Naya colors, since Naya is his homeland and we still need a Green/White Planeswalker.
Due to the release announcement page I half-recall, I'm predicting we'll get a new version of Garruk in M15.
I'm also predicting that due to Return to Ravnica being on it's way to rotating out, we'll have some multi-color-lands in M15 so they don't have to have them in the next theme set for when the Theros Scry-lands shift out, and also because of it having been a while since M12's dual-lands. This is a more tentative prediction, but I'm going to predict they'll be new ones, which feature color wedges (a color and it's two opposing colors) designed similar to the shard-lands (like
Seaside Citadel or
Bant Panorama only wedges rather than shards).
I also predict M15 will avoid any cards with X in their cost only blue or green and colorless, due to Wizards possibly having missed during playtesting the Kiora's Follower/Illusionist's Bracers combo, and wanting to limit it's impact on Standard.
I also predict M15 will try to have a cycle of 'cheap' low mana cost variants of iconic monster tribal creatures of each color, possibly with some kind of drawback or growth element or something to allow them to still be 'big' creatures, a Sphinx, Angel, Demon, Dragon, and perhaps something normally big that is green, not sure what there, maybe a Treefolk.
I also predict a low mana cost blue creature with hexproof/shroud, since it's generally an ability shared between blue and green, and green got it's turn last time with that elf and witchstalker, and they want to keep bant enchantments a thing while Theros is in rotation.
I also predict they'll go for a cycle of 'off color' creatures from tribes normally found in other colors.
I also predict a cycle of 'exotic' tribal creatures from that are rare in other sets or only found in them, with some re-prints and some new ones, possibly including Kithkin, Soratami/Moonfolk, Duathi, Viashino, and maybe Centaurs.
I also predict a Birds of Paradise reprint with new art, as the art I think used in previous 'M' sets was originally from the original Ravnica: City of Guilds, and we just recently had a Return to Ravnica and it wasn't reprinted there.