There is compelling cost saving marketing strategies made by Microsoft for companies to think about migrating to SharePoint online. No need for data centres and flexible licensing being the strongest reasons. But as of today is it practical? Security is the biggest concerns of enterprises but does the online product support features that are required to move organizations to SharePoint online. Let's see below.

Apart from any customizations, as on today SharePoint Enterprise online does not support the following features -

General Features -
  • Alternate Access Mapping (AAM)
  • Analytics Platform
  • Auditing of View Events
  • BCS: Profile Pages
  • BCS: Rich Client Integration
  • Claims-Based Authentication Support
  • Custom Site Definitions
  • Custom Site Provisioning
  • Configuration Wizards
  • Distributed Cache
  • eDiscovery
  • Full-Trust Solutions
  • InfoPath Forms Services
  • Host Header Site Collections
  • Improved Self-Service Site Creation
  • Managed Accounts
  • Patch Management
  • PowerPoint Automation Services
  • Quota Templates
  • Read-Only Database Support
  • Recycle Bin (SharePoint admin center)
  • Recycle Bin (site collection)
  • Remote Blog Storage
  • Request Management
  • Request throttling
  • Resource throttling
  • SharePoint Health Analyzer
  • SharePoint admin center
  • Shredded StorageState Service
  • WCM: Analytics
  • WCM: Catalog
  • WCM: Cross-site publishing
  • WCM: Faceted navigation
  • WCM: Image Renditions
  • WCM: Multiple Domains
  • WCM: Topic Pages
  • Word Automation Services
  • System Status Notifications
  • Unattached Content Database Recovery
  • Usage Reporting and Logging

Insights Features not available -
  • Business Intelligence Center
  • Calculated Measures and Members
  • Data Connection Library
  • Decoupled PivotTables and PivotCharts
  • Excel Services
  • Field list and Field Support
  • Filter Enhancements
  • Filter Search
  • PerformancePoint Services
  • PerformancePoint Services (PPS) Dashboard Migration
  • Power View
  • PowerPivot
  • Quick Explore
  • Scorecards & Dashboards
  • SQL Server Reporting Services (SSRS) Integrated Mode
  • Timeline Slicer
  • Visio Services

Search Features not available -
  • Advanced Content Processing
  • Content Search Web Part
  • Continuous crawl
  • Custom entity extraction
  • Extensible content processing
  • On-premises search index
  • Refiners
  • Result sources
  • Search connector framework
  • Tunable Relevancy

With so many features unavailable, only plain, vanilla out of box installations can be moved to SharePoint online which will be very limited enterprises, probably just small and medium sector organizations or simple websites. Lot of features need to be available to move the entire data corpus to SharePoint online.