I sent an email to sixt and asked about the platinum card. the reply was that the platinum program will still be available as it has been in the past. LH SEN, however, get a voucher to get a sixt platinum card.
I think this also means, that the rule 20times renting in a year equals getting the platinum card doesnt work anymore. this is the only thing I guess that doesnt work. or they do it automatically by computer system at the end of the year.

however, I think it is good, that they limit the number of platinum cards a bit, as it didnt really seem to be exclusive in the past anymore. (in the contrary to the europcar FIRST, which is rare and gives 3-4 classes upgrades, not 1 or 2 like Sixt)
or they give the really heavy renters the Diamod
thats never gonna happen