Why do all option builder structs take Buffer or Window arguments by moving?

[dasupradyumna]

For example, if I create a buffer / window and want to set options, create autocommands and commands, then when I use the corresponding option builder structs for building the option structs, I noticed that Buffer and Window are moved into the buffer() and win() methods. So I have to use clone() every time I want to use these.

What is the motivation behind moving them and not passing them as a reference?
I believe passing them as references would simplify the user API. Are there any demerits to this?

[noib3]

The bodies of the functions you pass Buffers and Windows into operate on owned instances, so it would be suboptimal for them to take e.g. a &Buffer only to immediately clone() it.

There were talks of making Buffer, Window and TabPage Copy types, which would alleviate the syntax burden.

[dasupradyumna]

I see, that makes sense. Was the conclusion of those talks to proceed with making them Copy types?
Are there any plans towards implementing this?