> What advantages does it have over TCP?

Significantly simpler implementation.
Lower overhead, giving better speed over local links.

Also, although not an advantage of IL per se, there are a few
advantages to Plan 9 having another protocol in the stack,
especially one which can run 9p. It helps guard against any
accidental network-dependent creep.

> Does it worths the effort of tailoring it back in,

It's not hard to get back in. Erik's 9atom has it. Whether it's
worth it or not is hard to say. I like having it, but NAT boxes
(and occasionally non-NAT routers, although that's more
rare) can cause problems. It is slower over common wide-
area links (lacking TCP's congestion control).

> esp. for a fossil/venti site?

It's mandatory if you want to use kenfs; it's entirely optional
in a fossil/venti (or cwfs or kfs or whatever) environment. It's
sort of depends what you want from the system.

Personally, I'd suggest doing it if you have multiple systems
on the same local net for the pedagogical benefits alone.

Anthony