Thanks for your suggestion.
We have already considered this and would like it (it’s on our “projects that would be nice to have” list), but it would be an extra app because it’s in no way related to CalDAV.
Personally, I was very confused by people mixing ICS subscription and CalDAV synchronization although those are two very different things: CalDAV is a complex protocol based on WebDAV, there are features like appointments and invitations etc. Much of DAVdroid’s code is dedicated to the CalDAV protocol.
It should however be possible to use some parts of DAVdroid for ICS subscription.