[Leica] Retrofitting meters to earlier M models?

[Mike Dembinski <mdembin@it.com.pl>]

Since I bought the M6, the older guys just sit on their shelves in my camera
display cabinet, awaiting their monthly winding-on and shutter-release ritual.
The battered M2 gets the occasional airing, along with the equaly battered
Super Angulon, whenever I need coverage wider than 28mm. The near-mint M3 has
become a museum piece together with a 50mm Summicron of similar vintage, now I
have a new 50mm Summicron-M. The M4, it just sits there.

My point is this. Surely it is not beyond the wit of Leica Camera to retrofit
M6 light meters into earlier M bodies? Hell, I'd give up the D/A for a meter
any day. Any reason why this can't be done?

An old question that has been done to death on this group but I've missed due
to my relative newbishness?