Hi @carstorm,
There's another thread here where we're talking about cPanel compatibility, which was at
In general Let's Encrypt will often require some level of support from a shared hosting provider, and we hope to talk to many of the hosting providers to make sure that they take whatever steps are necessary to achieve that support. There may be some configurations in which hosting providers already allow users to deploy certs without the providers' intervention; in those configurations it may be possible for a shared hosting user to get a Let's Encrypt cert and install it manually.
It will almost always require the provider's assistance to allow the process to be automated on the provider's infrastructure (for example, installing the cert automatically or renewing the cert automatically).