> It is even more likely that the user will use some serialization

Serialization is beyond the scope of what I am talking about. I am talking about reading bytes from a serial port.

> In that way, when using Async for network sockets, the SerialPortHW concept wouldnt be involved at all

But that is my whole point about Asio being split into smaller libraries such as Asio.Core, Asio.Network, and Asio.SerialPort. So you can use Asio.SerialPort without needing Asio.Network.

> in many occasions such extra async framework or the streams are not used.

You didn't read and write bytes to the serial port? What did you use it for?

> it would be in a different concept not included in the current project.

Its important for the library to implement the same "concepts"(or type requirements) for better consistency and composability(the only exception is iostreams which is horrible for both usability and implementations).