Perhaps there is more.
What about an 'realistic' platform independant interface.
Reality (for the moment) is:
OS/2 - OpenDoc
MacOS - OpenDoc
Windows - OLE 2.0
UNIX - i don't remember a name, but there also a OpenDoc-like interface
A few issues for such a modular Browser:
- (Inter)action on client side
- Style sheets
- Layout control
- Proxy-control (resolving host-moving-problems)
- Downloading (and auto-installing) of small patches