I would guess the first question is: What EXACTLY do you want?
You have to precisely define what the system you want would do and how it would do it. If not directly in technical terms, by describing the idea with your own words.
Right now, nothing forbids any user to write down a receiving address in his profile. Except maybe the rules of some forums. That’s pretty much all is needed. This is crypto! People can publish receiving addresses freely and senders can send to it without much privacy concerns or other nonsense involved.
Sure, if you use an on-chain address, transactions are public and using the same address for everything is far from ideal. But you can use the LN with BTC, or an exciting new development which I hope will gain traction: PayNyms. Or you could use a privacy coin like Monero.
By doing pretty much nothing and by just promoting a certain usage in a community, people are free to use the coins/networks they want. Several of them if they want. Click on my nickname and see for yourself. You could set up a special box for this, and maybe specifically ask to people to fill it in at registration. Here, I hijacked the “pronouns” section. And I used the website box to publish my PayNym. In any case, things can be entered directly in the “About me” box.