Work with coffee long enough, and you'll try things. I suppose it's the same with any endeavor, but coffee is the one with which I'm most familiar, of course. In any case, however captivating the basic tasks are, you'll inevitably be motivated to step outside of that routine, and to try things. Things that might sound awful, and might be just that. But you never know unless you try.
Today, that's what I did.
A preface, first of all - or perhaps a justification. I take my coffee and espresso black, and have no real desire to do otherwise on a consistent basis. Still, many people do use condiments; cream and sugar are the most ubiquitous. The intrepid barista - perhaps searching for a competition worthy signature drink - might try other things.
So we're clear, putting something in coffee is not uncommon. Not that anyone would contend that it is, of course. Putting something in the portafilter with espresso is less normal, except for turbinago sugar, in which case you've got a "Cuban". But still, this is an acknowledged drink. It's on the occasional menu, and any barista worth their salt will know how to prepare it, if ordered.
Speaking of salt... It doesn't work so well, when added to the portafilter, and pulled with espresso. In fact, the result was truly awful. I sipped, cringed, then managed another bit. Then I tossed the rest, unable to imagine finishing even the ~1.5oz that remained.
But you work with coffee long enough, and you try things. Dreadful, horrible, palate blanching things.