I really don't understand the attraction of "making the one thing."

Chrome/ChromeOS and Android are very different. Neither is going to supplant the other.

They also have some clashing goals: Chrome wants to be more security paranoid than Android. In theory Google can find Android malware authors, cut them off from access to Google Play, and kill bad apps in the field, while Chrome is exposed to both malevolent and hacked Web sites.

I see harmonization as more of a product management activity than any particular technical choice.