Please keep Kaiten.
If they really want to reduce button bloat, I'm in favour of merging some skills that are either mutually exclusive because they can only be cast one after another or because one is for single target and one is for aoe.
Shoha I & Shoha II, Guren & Senei, Iaijutsu & Tsubame, Ikishoten & Ogi Namikiri would all make sense to merge with Iaijutsu and Tsubame not even losing us any fancy animations some people may like.
Kaiten added a small amount of Kenki management. It wasn't huge but it was there and if you have an AST in your group it added even more nuance because dumping as many Shinten as possible in a card buff without losing Kaiten for finisher moves requires a bit of attention. It flowed well with the rotation and I found it a fun ability (much more than pure Shinten spam). Animation and sound is a bonus point for me.
But most of all I don't look forward to Shinten spam as the only spender.
Bunshin doesn't require a huge thought process either but it is something to keep track of over just using Bhava when you're about to cap.