I would propose medium to high level spider monsters have 1-2 silk as a fairly common or uncommonish drop (not sure how drop ratios work)
The reason for this is that Herbalore does not yield very much silk from my experience with the skill, and honestly that's fine. However the overall comparison of Merinium vs Heartwood vs Silk- Silk is pretty hard to come by, adding it to drops for Spider monsters provides a little immersion it is also a simple task once approved to add to the drop tables.
I stand to be corrected if wrong but I believe monster drops are on the "to do" list for "time in the future" or "there is not enough time in the day" to look at more closely. Your proposal can be part of that which will be looked at I'm sure. And Welcome
I like the idea. Just for the sake of fun, I would even rename the silk dropped by spiders to "Spider Silk", but we need to check for that if the currect crafting script has no exclusion of items with special names.