Some people go all the way down to 1 or 2 bars (soup espresso). I've mostly seen it in the context of very light roasts and I tend to buy darker roasts so I really haven't spent much time investigating it.
I did see a video on americano's recently where steaming the water to heat it rather than using a kettle or water from the espresso machine's boiler made a better drink. That does intrigue me and I'll probably give it a try this weekend.
Lately I've been making mostly decaf and it's really hard to get a good shot no matter what I try. Drip coffee comes out great, but my decaf espresso always seems to have a real harshness. Beans are fresh and my water is good, so I'm thinking it's time to replace the burrs in my grinder.
> steaming the water to heat it rather than using a kettle or water from the espresso machine's boiler made a better drink
Was it Mr Hoffmann[0]? He has a decent explanation for why this might be the case too (and does an experiment later which points to it maybe being dissolved gases.)
1-2 bars isn't really espresso, it's a moka - which can be quite good in its own right. It falls into the genus of pressurized brewing though, so same genus different species. There's a no man's land from 3-5 bars that is not really used and might be worth exploring, but most 'standards' consider 6 bar the minimum to be a true espresso.