My thoughts on Spellbook in the bot lane
So, TP sivir(Which has now even made it to LCK, being picked Twice in Week 1 by SKT and King-Zone). The reasons for her use are: Picked due to her wave pushing ability, allowing her to shove waves in to the enemy adcs tower, aiming to make them miss cs due to the difficulty of last hitting under tower when under pressure from poke. This summoner lets her take heal at the start of the game, so she can push until she is low mana/hp with safety, then return to base after 2 minutes, exchange the off cooldown heal to Teleport and use that to return to lane to keep up the constant pressure. This reduces the available backing window for the enemy lane and provides map pressure for the ally jungler to invade along side the support being able to get vision control of the river/enemy jungle. Sivir then swaps back to heal on one of her next bases, likely only using Tp once, or twice possibly to get mid/top tower before the enemy bot lane have any chance to rotate Used with the Relic-shield ADC strategy which you can learn more about in my other video, linked in the description!
Sivir also uses spellbook for the same reason that some other adcs are taking it right now - Lower summoner cooldown for increased safety during lane, easier positioning in fights, and less likelihood to be picked off late game before an important moment.
Current possibly users are(all generally immobile) - Kog maw, Tristana, Jinx, Twitch, and Varus. However, many pros are still preferring either Fleet Footwork or Press the Attack depending on the champion, so this may not turn out to be a shift in the meta as few pros are sticking with the Spellbook strategy.
Finally, Supports using spellbook: Current users - Rakan, Alistar, Blitzcrank, Leona. All who rely heavily on their flashes to catch enemies out of position. All of these champions use the rune to lower their summoner cooldowns by 30% and make more plays using them, with some even adopting Boots of Lucidity on top to gain an extra 10% reduction, reducing flash cooldown to 180 seconds!
However, the majority of these supports currently prefer either Aftershock due to it’s high damage, or Guardian to provide safety for their ADC. So it is unlikely Spellbook is used more unless these are nerfed.
Let me know what you think of the strategy, personally I hope it stays around.