.corp, .home and .mail should also be perfectly viable for private use after ICANN eventualy decided to cease all processing of applications for those TLDs.
"Whereas, on 30 July 2014, the ICANN Board New gTLD Program Committee adopted the Name Collision Management Framework. In the Framework, .CORP, .HOME, and .MAIL were noted as high-risk strings whose delegation should be deferred indefinitely".[1]
Deferred indefinitely is not quite the same thing as reserved for private use. For home use cases it's probably good enough, but a corporation will want more assurance than "the current ICANN has stopped processing applications for this TLD."
Actually, if history is any indicator, we can’t trust any of these companies with this. Remember the org tld private equity fiasco? ICANN only did something after public outcry and EFF interest.