The Synfig exported animation will be a Godot Engine scene that the root node will have the format Node2D and the scene’s file extension will be .escn. Blender already has this plugin that exports.
Hi and welcome here 
It is not sure that such a plugin could produce a full featured export from Synfig.
Also an export to .escn would not be necessary the best option, as glTF is recommended.
If anyone is interested in this, here are some sources:
Common
Import Process in Godot 3.0+ (Godot Docs)
Importing 3D scenes (Godot Docs)
.escn
TSCN file format (Godot Docs)
Blender ESCN exporter (Godot Docs)
godot-blender-exporter (Github)
glTF 2.0 (recommended)
glTF 2.0 Specification
Good luck!
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