I think this is a bad idea.
There's a lot of difference between the 40uV/C of a type K thermocouple and a standard 4-20mA loop commercial system. etc for the various other requirements.
Analog muxes can handle the first, though you also have to provide cold junction compensation, but their high and unpredictable resistance make the second more difficult if used on the same input..
etc.
If you want to design a proper product to handle this, you'd better either get learning or employ professionals of some experience.
Are there products of this sort on the market already? - and if not, why not? sounds like a nice idea..... you can't be the first to think of this.....
Maybe because is isn't easy. And probably not possible without some compromises in performance. And much more costly than standard solutions.
And to what gain? Such that a wireman can wire all the different types of sensors randomly, rather than to various specialised inputs? No big deal - tell him to follow the drawing.
Bill your client and get out quick.
Allan