Unless I am missing something, you're describing a budgeting app, and a lot of those already exist. Granted, no good ones that are FOSS in my experience.

I find it odd to use a wallet as a budgeting tool. Although, it could be useful to connect it to a separate tool that multiple wallets/addresses can connect to. This solution works for individuals and groups (families, businesses, etc)

Having a secluded wallet with the same functionality would be redundant and make less sense beyond a single user. I also think it's better practice to separate the major functionalities for modularity and codebase management. I generally think it's a bad idea to bloat wallet software.

It makes more sense in my mind to have Bitcoin focused budgeting software that can somehow watch transactions in a private way and categorize transactions automatically using text input on the transaction or manually if you choose.