'email may never come back on-premises' ?
Outside the US, and with regard to the very long arms of the Patriot Act, there are many regulated market sectors whose data-security risk assessment keeps them well away from any US-domiciled service providers... and then there is the EU, with its new General Data Protection Regulation, which also constrains many sectors to keep the majority of their data [and data flows] well away from the major cloud service providers.
Many applications not handling personal data -are- suited to migration to cloud services; many are already hosted somewhere by service providers hurriedly re-branding their hosted service as a Cloud Offering... but until there is clear legal separation between in-country operators and their US parent brands that offers true protection from data access by DHS, acceptable to regulators, many markets will ignore the benefits of cloud.
or local companies provide the offering. I'd think this will happen in conjunction with some companies working to provide separation from US government agencies