I believe your idea of adding use registrations is a very bad one.
Let me preface by saying that,
a) I do realize you have 100k+ users and can afford to not care
b) I will mention other similar services in this post, but I'm not a shill or endorsing those
c) SG support you no matter what, just for the fun of it
The beauty of FaucetBOX was that one could use it without even realizing he was using it.
(Hell, I can use FaucetBOX to send you bitcoins right now, and it will work, without you even having to learn what FaucetBOX is.)
Many newbie faucet users do not initially understand where are their satoshi going, assuming they will just end up in their wallets. As they eventually do! Some users can become worried and visit the "address checker" page. There, it explains the whole dust transaction ordeal, shows the progress till threshold and lists the latest payments. At this point, the user get an "a-ha" moment, it clicks, and FaucetBOX takes it rightful place as a middle-man in his mind.
An ideal faucet contains 1 address field, 1 captcha and 1 "CLAIM" button, with no redirects, no account sign-ups, etc (Such a faucet might not exist in this world). One page load, one form submission, one "drip". Your system complicates it by 3 extra steps, at best. At worst, it would just drive the poor user away. Now he has to learn what "faucethub" is, what a "faucethub account" is, which one is which, and why is that scary-looking number is even needed, if his "address" is just his email?
Then, you system kinda breaks the automation aspect. If I get error 456, there's nothing I can do about it without human intervention. For automatic payouts this is really problematic.
Case in point: let's say I want to migrate my faucet website with many referral users to FaucetHub. In a "perfect" migration situation, I would just start sending their satoshi to the new website, and the net effect would be the same. But with your new system, they will first have to become worried that their payouts have stopped, then investigate each and every site, create faucethub account, etc.
In a more philosophical terms, this systems abandons lots of good ideas bitcoin (and faucetbox after it) brought into the world. One of those ideas is that "accounts" are a meaningless archaic concept, that linking identity to a wallet address is futile and counter-productive, and that if you need to prove anything, you should use crypto (such as message signing), not privacy-intrusive methods like ID scans or email addresses.
I think it was really beautiful, that faucetbox pages worked as-is, with any possible bitcoin address, right out of the box. The fact that they were public to everyone reflected the fact that blockchain is public to everyone. Doing something meaningful to those addresses (changing the threshold, effectively requesting a withdrawal) was only possible if you had a private key, reflecting another important bitcoin idea: you can still retain control over what's publicly accessible.
Don't get me wrong, I'm not saying all bitcoin-related sites should abolish accounts or off-chain transactions, I'm just saying faucetbox was getting the spirit of crypto. That account thing you're doing, it really doesn't.
What's worse, your system reduces the bitcoin address from a primary identifier to an attribute of a faucethbub.io account.
Why even ask for a wallet address at all? Arguably that's a waste of time, if your intention is to get to faucethub account name. And those are easier to remember too, so why not go all XAPO on our asses and just use that?
And to circle this back to the automation aspect, I would argue that letting the transaction pass, and keeping the coins in some kind of the "future" wallet is a more convenient way to do things for both faucet users and owners. Consider the:
hey, 1bitcoinAddressHSH, you just got 12 satoshi, but you can't withdraw them before you signup here, haha!
approach. That's what PayPal is doing (for credit cards vs email addresses) and that's what XAPO is doing (as far as I know). Or maybe it's a kind of a lose-lose situation, only to be solved by not having any accounts at all.
P.S. What happens when someone else gets my address linked to his account? Can I reclaim it using the message signing?
P.P.S.: How about an immediate ref.payout to a non-faucethub-approved BTC address?
Sorry for the wall of text, hopefully I've managed to express myself fully without angering you too much.
TL;DR accounts bad ; error 456 small yet deal-breaking change to faucetbox API