SirPrimalform: Arguably the most popular 'chiptune' style chip ever thanks to the C64 demoscene (and some awesome game music like Monty on the Run). Apparently though it would be really hard to reproduce nowadays because it used a silicon process that was really 'dirty' and hasn't been used in a long time (I believe it was outdated even at the time of the C64's introduction). If it was reproduced now using modern processes, the analogue parts of the circuit (the filters) would actually sound
less like a SID than a software emulation does, which is why people mostly do software emulations when trying to clone a SID. Without actually using the shoddy and vastly out of date process (which no factories use now), it's basically impossible to do an actual clone.
I don't know that it would be impossible, but the end product would certainly be of a significantly more uniform quality than the original SIDs, that is true. Not all SID chips sounded the same, due to the inaccuracy of the production process for the analogue filters (as you say). In fact I own
this CD, which only exists at all for that very reason. Martin Galway, the composer of such renowned C64 music as Wizball, Arkanoid, Green Beret, Comic Bakery, Ocean Loader, etc., originally selected a specific SID chip from a wide array of them for his own machine, to use in making his music. The CD, Project Galway, is a selection of his tunes played on his original C128D, containing said SID chip.