Create lightweight package AbstractDualNumbers or ForwardDiffBase or similar?

My apologies if this has been suggested before:

While ForwardDiff is not the heaviest of packages in the ecosystem, it's also not exactly lightweight (take 1.6 seconds to load on my system). A lightweight package AbstractDualNumbers.jl or ForwardDiffBase.jl (or similar) that just defines something like abstract type AbstractDualNumber{Tag} <: Real end and things like function AbstractDualNumbers.value end and function AbstractDualNumbers.partials end could allow packages to define custom push-forwards without depending on ForwardDiff itself.

I know that there are exciting efforts underway in the Julia-AD-ecosystem for new ADs (e.g. Diffractor), but ForwardDiff is certainly not going away any time soon. A really lightweight way to define push-forwards could reduce the frequency of @require ForwardDiff in the ecosystem quite a bit, and also make it possible to move code from packages like DistributionsAD to Distributions, etc.

No implementation files or tests are identified. Start by reviewing ForwardDiff's public dual-number interfaces and the proposed AbstractDualNumbers or ForwardDiffBase scope; the issue would need a settled package name, API, and adoption criteria before completion can be assessed.