Most of the "no marker" sidequests in BotW that I remember are largely collectathons; find enough wood to buy a home, find weapons to show to a kid, find ten lizards to trade for some armor, find five frogs to show to a kid, find various torches around town to light, find ten pieces of flint, etc. I feel like these quests are basically equivalent to something like the hide n' go seek quest in Witcher 3, or asking of importance in a city for information in Fallout. I don't really care so much about whether these quests have an area of effect or not, because there's not much of a sense of discovery for just collecting a certain amount of something that's generally at least relatively common.
On the odd occasion that BotW does hand out a sidequest that's more about discovery (I really enjoyed the "hunt a monster to get the ingredients for medicine" sidequest, for example), I think it works pretty well, and I wouldn't mind seeing it implemented on a larger scale in a potential sequel or another open world title. With that said, I suspect implementing quests like these on a much broader scale (i.e. you have to look for something in a very specific area that can only be found by using the clues given to you) would require a sizeable amount of work on the dev's part. Writing hints that are both sufficient without removing all semblance of thought from the process can't be easy.
