This one topic has a lot of noise/smoke/lack of clarity around it.
So, here is the real deal,
- Sandbox solutions are not dead.
- However, sandbox solutions that contain assemblies running on the Sandboxed Code Service (aka - SPUCHostService.exe), are indeed deprecated and therefore dead.
In other words, sandbox solutions that are declarative – you’re welcome to use them in SP2013.
Quote from Richard “declarative solutions are very much still in play and widely used internally by SharePoint (ex: Web Templates and Design Manager). A declarative .wsp package (one containing no assemblies) is a powerful way to provision elements into the host web. So don't be afraid to leverage the solutions gallery as long as your .wsp packages don't contain code.” (source)
Furthermore, It is encourage to not do extensive tweaking of host web through code (e.g. creating new lists), if only because the install/uninstall/upgrade story of such artifacts becomes the responsibility of the developer and therefore cannot be consistent across apps.It is appropriate for internal apps (not marketplace apps) containing programming logic and host web dependencies.