I've been musing over the whole foxtailing thing ...
It "ruins" the look of the buds, and it makes a nice trim a lot more difficult. yes. But ... most growers eventually stop really caring about a close trim for their own stash. Y'know what I mean, fellow growers?
So, meh, got some extra leaf matter, so what. Just crumble it off the bud when you smoke it. I have more weed.
As far as stress and the role it plays, again, yes. I'll get foxtails from genetics, usually. I like to smoke sativas, and usually they can be a pain in the azz. They don't like it when they don't get pampered enough. They like humid and hot - equatorial stuff. That's a hard environment to produce and maintain.
But there's something to be said about stress, too. Stress can be good if you manage it right. For instance, there's a 420 thread about detailed studies based on drought, and he documents his own experience, with measurement, etc. There are stages in a plants growth where trich production benefits from some parching. In my garden, I find that I get a better final push, if I get careless with the watering the last few weeks. And we know that it's MUCH better to underwater a pot than to overwater. A totally limp plant will perk right up after you water it. A soggy one will be a mess for weeks. Dry soil can be good. It promotes root growth, and it also allows gasses in the soil to be vented and exchanged.
So, if a plant will foxtail under stress - and that can definitely be the cause (light stress or daylength, low humidity/VPD, lockout, etc) - foxtailing isn't necessarily a negative reaction. You just have to be sure that the buds aren't decaying or the new growth isn't fat with trichs.
Many of my hybrids and sativas will foxtail, mostly because my room is drier than they like, and I run 11/13 all the time to keep the other strains happy, and I'm in no hurry to chop and ugh, trim. I've had some grow 2 inches long.
It was a pure sativa - Destroyer from Cannabiogen - and went 14 weeks? in bloom before I decided to chop it. No signs of slowing down - didn't really grow many annoying leaves. It was
really fine herb.
Anyway, yeah, it depends.