Here is what BMW stated earlier, "There are no plans at the moment to build a lightweight CSL version of the M4, but there weren't any plans to do the last generation CSL either." That is completely correct, there were no plans for an E92 M3 CSL yet the hardcore M3 GTS came about later. No matter what it is called whether it be CSL, GTS, etc., BMW is at least leaving the door ajar for a hardcore, lightweight, and track focused M4.
Should this car come about it would weigh in the 3086 pound or 1400 kilogram range. The F82 M3 is already lighter than expected so where further weight would be shaved to this degree is something for the engineers to figure out. Expect at least 100 kilograms less than the F82 M4 which is currently stated to be in the 3306 pound range. Expect the car to seat two, have a rear seat delete, and a roll cage. A slight power bump would of course be included just as the E46 M3 CSL and E92 M3 GTS showed.
Keep in mind, this is all unconfirmed. The report detailing all this information cites an unnamed source at BMW. When an unnamed source with unconfirmed information is cited BimmerBoost is leery as Autoblog already showed us what unnamed BMW sources with conflicting information are worth and that would be just about nothing.
Is this just a publication reaching for buzz, links, and traffic again? On one hand you have BMW on record stating there will be no M4 CSL model although they do say things may change. On the other you have an unnamed supposed M executive providing details on such a model which would already have to be in the planning stages. Where is the truth? Somewhere in the middle. One thing is certain this car would be a great way to celebrate BMW's history.