The main “wasted” resources here is storage space and maybe a bit of RAM, actual runtime overhead is very limited. It turns out, storage and RAM are some of the cheapest resources on a machine, and you probably won’t notice the extra storage or RAM usage.
VMs are heavy, Docker containers are very light. You get most of the benefits of a VM with containers, without paying as high of a resource cost.
If you just want read-only access to seafile, you can use the FUSE extension, but it only works in read-only mode.
For OCIS, look at the POSIX driver, which stores files in a normal directory structure.