Hey Farshid,
Since a plugin already exists and there is a niche market for this feature, we more than likely will not make this a default engine feature. The industry standard uses a different workflow to control the lightmap density relative to the scale of your meshes in the scene by manually controlling this on a per object/mesh basis.
https://headcrash.industries/stories/why-your-idea-might-not-make-it-into-ue4/
Thanks for your time and let me know if you have further questions.