"What would also be really cool, is using format also dynamically in the horizontal direction. That would probably mean to use eval and hook into the lowlevel formatting, I guess."

You would need eval but shouldn't need to mess around with *STEP{FORMAT} or anything like that. There's an example in "perlform: NOTES"; search for "The truly desperate can ...". :-)

I used to use format quite regularly 20-25 years ago (probably a couple of times a week for generating all manner of reports). Although fairly proficient back then, I often encountered pulling-my-hair-out-in-frustration situations. These days, I'd generally look to other solutions; I don't think I've used it this millenium.