I have always wondered why the manufacturers don't dwelve more on this. Is it not a desirable feature? I would say it is, at least for me.
While on automatics a longer power reserve (longer than 40hrs I mean) is not necessary for most, although even in that case I believe a power reserve long enough to keep the watch "one" from Fri night until Mon morning would be perfect, in the case of mechanical watches it is even more so.
Are the technological hurdles so great to achieve this? Would it put too much strain on the parts ? Size-wise, with nowadays watches becoming more and more wrist-clocks than wrist-watches, there shouldn't be a problem, plenty of space there to add extra coil(s).
So what is it then?