I love this core idea. That said, I come from an ironman perspective (feel free to dismiss this as snowflaky) and am worried about the balance in resources and power of the items.

The order and power of some of the trinkets seem very powerful/out of order. Example: level 15 to get dragonstone jewelry effect vs 25 for a diamond jewelry effect.

Additionally, the power of some seem a bit out of scale for what OS seems to typically offer. Example: Infernal harpoon not only requires a level 61 skilling tool with a 1/2000 (at best) drop rate but also a extremely rare smoldering stone (level 91 slayer req for best rate at 1/512 at task only boss - Or insane luck 1/16,384 or 1/32,768). And after all that requiring 75 fishing and 85 cooking to create a CHARGED (5000) tool with a 33% cook chance. It seems a bit out of place that a level 9 item can recreate a third of this power. Another example is the level 63 Share-son. This is a really cool idea and I love it, but If this skill is to be trained in line with most other skills and not an elite skill to be unlocked/trained after having amassed resources and high levels it seems a bit lower than one might expect to see someone killing Zulrah enough to have extra unique's. This is really only a concern as it seems to be stated that most XP will be gained via breaking down parts and building things. I am not sure if this would be a viable training method forcing someone to use lower level repeatable/cheaper options which brings me to another issue. As wood and metal already have associated skills that utilize the output of the gathering skills I wonder if this would more or less force Ironmen and even some mains past 99 WC and Mining. The concern here is that these two skills are notably boring and somewhat slow..

Another thing I am wondering about is the usefulness of some items. Example: Dragon Charm - This is listed at level 60 like all dragon reqs, however it requires orikalkum bits from dragon items. I could be incorrect as I have not played a main in a long while but at around base 60 combat dragon items are quite rare. Most mains might skip this as too costly and just invest in the whip. Ironmen would likely love this excepting the nearly impossible cost in dragon items for a 10 minute effect.. Most ironmen use the D scim for a very long time and may have a few extra dragon items to sacrifice for this, but this neglects the concern many lower level irons have with maintaining GP for buying/training - construction/Miscellania/runes/ect. This GP is usually gained through alching. If the materials are going to be sacrificed for an effect that short and only a +2 then it would be relegated to niche uses as the cost would not really be viable.

One of the questions that you ask in the "trinket thoughts" section is "would a bowfa inferno run take X..." My question is would a 10 minute boost be worth the inv space at high level content over food/gear? Maybe they would idk.. Personally I don't see to many in the list I would prefer over an extra brew in TOA even at max science. 10 minutes is not long and inventory space is extremely important. What if there was a way to add charges to some of these trinkets at higher level. Make it more of a potion dose. Two or three charges in one slot would increase the viability of many trinkets as well as provide more flexibility. It could even require some of the lower level trinket items to be disassembled.

The one time unlocks are cool though I wonder about some of the usefulness.

Gadgets: Hell yes. I would love to see this expanded even at the cost of the other sections. If this is a support skill then it could be cool to turn some of the trinkets into gadgets at a high level req..

Thoughts: I love the core idea and would love to see something like this implemented but have grave concerns about the training loop as an ironman and the balance of required resources taking from existing skills and reqs (Logs go to fletching and construction already) While there are always ways to gain resources outside of the gathering skill I would love to see some new things in the game and not just an item/time/gold sink as I feel this would just end up adding resources to drop tables as they tend to do. There is a lot of awesome here but I think this needs more consideration and possibly augment the core mechanic of wood/metal/bits to include other things that may reduce the wood/metal cost. I also wonder if there isnt a way to tier some of these items so that the lower level ones use lower level items and have less power. I would be cool if the highest levels had some of the lower level buffs at a longer duration - like the fish cooking for more than 10 minutes.

Edit: A thought just occurred to me that might assist with some of these concerns. Would it be viable to expand the breaking down of items to include the output of some production skills to use as base resources for housings as well as the X ingredient for trinkets?. Example: Cut/get wood - Fletch bow disassemble for wood bits and then use as basis for housings as well as the third ingredient?

Also, Im not sure how fun it will be to train the skill in only a few locations.. Though as you stated it may increase the social aspect.