I just created a Python 'safebox' component where it can connect to any relay for proof storage and any mint for issuing/redeeming tokens. 

The safebox can receive funds via the mint and send funds to any lightning address.

The only thing 'local' for the safebox is the nsec, which you can pick up and take anywhere. So long as you know the nsec and know the relay(s) you have access to your ecash.

This is based on NIP-60/61 by nostr:nprofile1qqs04xzt6ldm9qhs0ctw0t58kf4z57umjzmjg6jywu0seadwtqqc75spzpmhxue69uhnzdps9enrw73wd9hszynhwden5te0wp6hyurvv4cxzeewv4eszynhwden5te0wfjkccte9enrw73wd9hsxv8qkt and I am adapting for my 
own backend requirements of a 'custodial wallet' for a payment system.

What is wild is that the 'wallet' instance can operate and exist contemporaneously across multiple jurisdictions.

Anyway, still early days. Just excited to share my progress and insights. If you want more details, please DM me. 

 Yep. I just proved it can be done

nostr:nevent1qqsvjc7ud9vjnlnspl56eu02j79tj25px74nhn5mkfu4wjytxq337rgpzemhxue69uhhyetvv9ujumnfd4hjucmpwd5z7q3qq6mcr8tlr3l4gus3sfnw6772s7zae6hqncmw5wj27ejud5wcxf7qxpqqqqqqztr0j67 

 I am new to Nostr and maybe a bit out of my depth, but if you want to explain to me more in details how the system works that would be amazing.
It might be the beginning of the creation of the documentation.