I always treated proficiency with tool as a profession - it seemed to be what the rules indicated. So, if you are just creating a batch of new skills called professions that do what tool proficiencies do, ok. Only drawback is the house rule baggage to reach the same plsce.To answer a couple of questions:
1. The purpose is to fix the wonkiness between tools and existing skills like, Performance/instruments and medicine/healers kit. So, [MENTION=6919838]5ekyu[/MENTION] in that sense, I'd be trying to make it more West? Streamlined?
2. To shift the proficiency to a skill focus instead of a tool focus. Where the tool is just the a piece of equipment used with a skill, and not the skill itself. Yes, I assume that 'tools are a sign of professional training' but I don't like how it's implemented. The tool itself should just assist the proffession.
So, for Instruments, you wouldn't have a proficiency in an instrument. You'd have Proffession: Musician/Oration/Artist/Actor etc... and you'd choose an instrument. I'd drop Performance all together.
I'd drop Proficiency Healers kit and use Medicine (Proffession Healer), so there's no overlap.
***
I've skimmed XGtE and would probably incorporate some of the uses but, once again, I'd remove tools-as-a-skill.
[MENTION=6919838]5ekyu[/MENTION] Regarding uses, I was just thinking they'd lose a 'charge' on a 1- not every roll. But I like the idea of setbacks better. As you say, less tracking of resources. I'm not specifically trying to make Players track resources...I'm just brainstorming ideas. I just like the idea of needing to occasionally resupply. (rations, ammo etc...). Generally, I don't make players keep track unless they will be away from civilization for a long time and needing to track that stuff becomes part of the challenge to survive. Instead I just tell them to spend a few gold and say they've resupplied.
[MENTION=20564]Blue[/MENTION]
You aren't fond of a straight +2? Maybe, instead, better tools just let you do things more efficiently. Kind of in line with what [MENTION=27385]aco175[/MENTION] is saying. Drop the amount of time it takes to craft or pick a lock or whatever. Outside of adventuring, it lets you do more things with your down time - make more money - craft more stuff. While adventuring, things like picking locks a bit quicker could have a focus if you need to get that door open before the guard comes back - but it's pretty situational.
I just mentioned #3 because I like the idea of training(proficiency) giving you more than a mathematical bonus. It opens options that were not possible before. It's one of the few things I miss from 3.5. But 3.5 focused that rule on knowledge checks (DC 10 being common knowledge and anything higher than that would only be known by people who had skill in the knowledge area) I'm not sure if it's worth finding a way to implement something like that, but I wanted to mention it.
"I'd drop Proficiency Healers kit and use Medicine (Proffession Healer), so there's no overlap."
Healers kit is not a tool and has no proficiency. Its adventuring gear and has defined uses.
Whether it's called tools or professions or background skills, many systems have used this same basic mechanic to have one set of (generally speaking) adventuring proficiencies and another set of more background or sort of day job expertise to try and mitigate the drive to get as much as possible of the adventuring stuff at the expense of common sense stuff.
This intent is shown in the custom background as you can get two skills and two tools but not four skills.
If your goal is to de facto roll up tool proficiencies into skills and let tool proficiency slots go into competition with more skill slots in general, that's not an approach I would be taking in my games because i think long run it would lose fun and useful character definitions.