In future there will be a "next generation" Linux,
not microkernel, but also not so monolithic.
More modular subsystems, drivers will be easier to write.
Native sandboxing.
Deprecation of classic POSIX permissions, file ACL by default.
Rewritten network userspace tools,
everything could be declared in one file (like in the network equipment).
Yet another desktop server.
Desktop will respond near real-time.
Better audio experience, low latency by design, no more xruns.

And more...
Depends where hardware will go. Like another architecture?