Multi-backend refactor

[Titus-von-Koeller]

This discussion space is intended to centralize all general discussions around the refactoring as possible.

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Please be sure to post individual topics separately below, so that responses can be within their own threads, on a per-topic basis.

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All backend related PRs should be addressed at the multi-backend-refactor branch. PRs to multi-backend-refactor should be as atomic as possible, i.e. focused on a single type of improvement; so that they are easy to review and discuss in isolation.

You'll see further updates from the maintainers here in the next days.