My bet is Koome. Ouko tribe is DOA - he will be mere SCORK judge ala Ojwang. Maraga sullied the safe-pair-of-hands narrative despite being long-time insider. Ngatia you are right has Nzamba Kitonga problem: too independent. Koome maybe mercurial but not really a disruptor. Low-risk. She stands out more as a feminist than a reformist which makes her a good compromise. Mwilu demonstrated her independence under Maraga leading to her predicament.
Anyway anytime you tout someone as "great" it actually undermines them politically. Eg. your Samburu boy Lenaola is unlikely to be CJ soon: too brilliant, too independent. Maraga sneaked in because he was principally viewed as an intellectual lightweight.