Firstly, fish, thank you for getting in touch with the community as much as you have. It's always nice to see a developer interested in the opinions of fans. It can be a double-edged sword, of course, but I'm sure you know that. I've got a few thoughts about things that I'd like to share after reading the design document.
TL; DR from me about the changes you've proposed:
- Infinite level scaling seems unnecessary but could be alright, but it is not a good way of dealing with players losing interest in the game. Talking about that is the bulk of this post.
- I'm not a fan of hard-locking weapons behind levels but soft locking is alright, since it makes people consider what they want to spend their points on more without totally denying them access to a weapon.
- Changing the skill system is good in theory but simplifying it as much as you are proposing seems unwise, since it takes away the ability for the player to specifically tailor their upgrades.
- Being able to choose perks/modifiers that apply major changes to the game is an excellent idea and I'm all for it.
- I am really conflicted about leveling up stats through usage, since it's been done both well and terribly in other games. I'd suggest having usage of certain skills augment the level of skills upgraded through Juice, to get the best of both worlds: you can upgrade you arm strength with Juice, but actually hitting things would increase it further, or give access to melee-specific skills/perks that aren't upgradable or accessible by default.
(Note: the full post I had written here was really long, and I realized it would make reading the thread a pain, so I've moved the bulk of my reply to its own page. You can read it here: https://itch.io/t/1382074/regarding-the-proposed-infinite-level-cap )