I am with Mark H. on this.  While I appreciate the theoretical underpinnings of the status quo, I am yet to see data stored in binary that did not originate from decimal at some point.  I think 99.999% of all instances of 0x1.199999999999ap+0 in numerical data come from a conversion of 1.1 from decimal to float rather than an a result of a computation that is correct to 16+ decimal places.

In a well-designed system, simple things should be simple and difficult things should be possible.  Decimal(x) = Decimal(str(x)) is simple and what most users expect and ultimately need.  Expert users will always have Decimal.from_float, contexts, round and other power tools at their disposal.