Walter has plans to add ownership and borrowing to D https://dlang.org/blog/2019/07/15/ownership-and-borrowing-in...
Not sure what the current state is.
Re:D 2.096 and other news
by WalterBright on Wednesday March 24, 2021 @08:10PM
(#26574815)
I'll be talking about it at the April nwcpp.com virtual meeting. All are welcome.
Here is a library for smart pointers: https://github.com/atilaneves/automem
Some people were also working on a reference counted type (that'd replace the GC I guess?) a few years ago, but I don't know what happened to that, or if it did make into the language. There are a few open RC pull requests from 2019 on the d runtime repository.