Has any one heard if Marlin will chamber their 1895 in .500 S&W? With modern propellants it should beat the crap out of the old 50/70 load. Any thoughts?

No. The 500 S&W has a pressure rating above that which the Marlin 336/444/1895 action can safely withstand. Wild West Guns is producing a new beefed up action based on the Marlin 1895 for the 500 S&W. http://wildwestguns.com/EStore/MasterGuideOrder/WWG04/wwg04.html