Indices are the way to go for a whole range of programs - compilers (IR instructions), GUI (widgets), web browser (UI elements), databases, games (ECS), simulations, etc. It is however without borrowcheck guarantees.
Rc and Arc are definitely a bad way to avoid borrowchecker. GC is used because it is much faster than reference counting. OCaml and Go are experimenting with smarter local variable handling without GC. At that point they may outperform Arc and Rc heavy Rust code.
This is very nice article, objectively lists possible pitfalls.
It's however not quite that simple.
I am in favor of removing as, but then try_from needs to work with more types, for example try converting u64 into f32 without using as. It turns out to be very hard. TryInto does not work in single step.
Important aspect is performance. HPC code needs to be able to opt out of math checks.
Also Results and Options are very costly, as they introduce lot of branching. Panic is just faster. Hopefully one day rust will use something like IEX by default https://docs.rs/iex/latest/iex/
It has the same benefits as Results, but if error is returned in less than 15% of function calls, then IEX is much faster.
Btw. allocation failure in std returning Result anytime soon?
Rc and Arc are definitely a bad way to avoid borrowchecker. GC is used because it is much faster than reference counting. OCaml and Go are experimenting with smarter local variable handling without GC. At that point they may outperform Arc and Rc heavy Rust code.