How is the new BoTRK on Kindred?

Kindred is still trash

As someone else said, it's okay on them. Kindred was absolutely gutted from their Q damage, Q cooldown, W healing, Mark Generation, etc. to make them more balanced. Being an ADC jungler has proven to be difficult to balance, as Kindred used to abuse the old Sated Devourer and has always been able to kite the jungle monsters into oblivion. One of the more difficult problems with Kindred is that their Ultimate saves everything - allies, minions, monsters alike - and requires you to be proactive in order to keep a target alive. It's easy to pop it down to save a squishy from, say Zed's Death Mark popping them, however it's difficult to save someone from Kassadin jumping on top of them and chunking them out. It's an awkward situation where if you pop it too early the heal is very minimal and provides no utility for saving someone, and popping it too late means they're already dead and the Ultimate saves the enemy team more so than yours.

They're still a fun niche-pick, and BotRK synergizes well with their passive making them able to shred tanks and epic monsters (Dragon, Rift, Baron) insanely fast. They're no longer able to "target" someone with their Ultimate, so saving their team relies heavily on them being next to Kindred, who positions like a typical ADC - on the sides/backline - as opposed to someone like Graves who can maintain relative safety at close range thanks in part to True Grit and his massive raw damage. Often you'll see a Runaan's Hurricane run as well to make the most out of team-shredding.

You can totally rush it if you're skirmishing a lot and enjoy the Life Steal or are dealing with a multitude of tanks. The buffs to it as well as the cheap price-point have been a massive success, causing AD's such as Ashe (that normally would ignore it for Crit/Essence Reaver/other stats and items) to rush it. Kindred's %Health Damage (from Passive and E) combined with BotRK's Passive, Attack Speed, and AD will instantly threaten tanks, however they themselves have a difficult time reaching the backline as walking out of Kindred's W prevents them from utilizing the shortened cooldown of Q, and crushes their damage.

BotRK is good. Kindred is not. Play Graves instead, untill he is nerfed and Kindred's mini-rework comes through.