@Devs: Please allow us to travel at will between servers.

[Abriael]

You'll be able to change servers, you'll just have to buy a server transfer to do so.

Not necessarily.

Logistically moving from one server to another is not an instant and easy task.

It's already been done. Yes, it's an instant and easy task (relatively instant I guess, as it takes a whole 8 seconds of loading). It works like a charm, and none of the objections you bring is a problem where it has been implemented.

Seperate servers exist because for most games it isn't practical to have the entire populace on a single server cluster.

No. Separate servers exist because of limitations in server technology that don't exist anymore, making server segregation obsolete.

Games are moving away from it more and more. And it'd be a good thing for ARR not to miss the train and remain anchored to an obsolete limitation that players won't accept anymore in a few years.

There are ways to do it but the server software and client have to be engineered that way from the beginning, as it is a completely different architecture/design.

Server architecture and design is not set in stone. Other games change theirs on the run.