Effectively you can now do this; a PK index + INCLUDE all other columns in the table. This will be kept upto date without any need for manual reclustering.
Sure it's duplicating the table data, but it's functionally equivalent to the reclustering or rematerialising a view of the table methods that people use now, just without the hassle.
It's not going to be slower vs an unordered heap + a separate index that includes all the columns. Hence MS SQL implementation is superior. If you don't want a PK, then MS SQL offers you an undordered option.
Sure it's duplicating the table data, but it's functionally equivalent to the reclustering or rematerialising a view of the table methods that people use now, just without the hassle.