You could request this as an ArcGIS Idea but so far, at least for me, requirements like this have been easy to meet by just opening a new MapDocument object so I suspect it would not attract a lot of votes.
For example, when Selecting predefined ArcMap template using ArcPy?Selecting predefined ArcMap template using ArcPy? means a "predefined template" to be an MXD located in a Map template folder inside an ArcGIS installation directory, it should just need:
mxd = arcpy.mapping.MapDocument(r"Current")
(although there is no need for the r
before "Current" above)
to be replaced with:
mxd = arcpy.mapping.MapDocument(r"<path>\<template>.mxd")