So your answer would be?
I think the collards are a good idea, just pointing out a drawback. I always dread when I have to deal with brassica stalks and roots.
Oh another option would be winter squash, I think they may be tougher on the east coast though?
I mow off large stalks and the roots just become wonderful organic matter as they decompose. We’ve been trying to do as much no-till gardening as possible/practicable.
Last summer I knew I wouldn’t have time to tend the veggie garden and decided to cover crop it. I was able to get a 50 lb bag of buckwheat seed from our local Agway (one of the few remaining). It worked very well for what I wanted, namely to keep weeds down. I seeded in early spring, and in mid summer I mowed it down just as the blooms were fading before it set any seed. The day after I seeded it again with the buckwheat seed and mowed that down in the fall, again before it set any seed. It didn’t ad much organic matter, but it worked well to block weeds and my neighbors bees loved it. I found it required very little effort, I spread the seed with a hand crank seeder and it germinated without any need to cover it.
How about Fava bean? improve the soil and hardy to 21f.
Since your not expecting to manage it well, you could get a bag of Goya 16 Bean Soup Mix, $1.79 and just plant them all. just a random experiment to see which take and grow.

Another option that I have never tried, but I may try this year is Sunn hemp. Gets very tall, so that may be an issue, but it’s a nitrogen fixer, supposedly won’t set seed in temperate conditions and it’s tropical so it will definitely winter kill.
Three: sow, scrape in, go away
Buckwheat, soybeans, millet (fox tail is tall and pretty, the short one is bird proso). The tall millets are very pretty and some are grown as annual ornamental grasses. But I like buckwheat, plant 2 or 3 times.