Maybe that could be one good outcome of such an API.
Popups exchange long-term trust in your brand for short-term profits. Of course it's the case that if you pop a modal in front of everyone, your conversion stats will go up. But potential life-time customers who have faith in your brand and believe in your mission will lose trust in you quickly and probably never sign up in the first place.
For me, it always comes down to the primary rule of UX: if you wouldn't do it IRL, don't do it online.
You can ask for someone's email if they look like they're interested in something you're selling, but don't ask for it the moment they enter your store!
That could be the motto of most every modern MBA.
Think of it this way: if the site that you have long term trust for does this, it means the previous methods weren’t working. The ‘trust’ was broken.
Would love to see your advice applied to your own life.
Sure, money might come from long term trust, but long term trust itself, literally, does not pay the bills.
The lack of a Remote Strangulation Protocol (https://wiki.kluv.in/a/RemoteStrangulationProtocol) is a problem again.
What you don't realise is that x number of people join the list and x number of people tolerate being spammed with 'did you know we sell stuff' emails every day for the rest of their lives. x number of those people actually do buy something; likley the thing they intended to buy originally but joined the email list in case a discount code would be the subject of the first 'welcome' email because this is what they have been trained to expect.
All this has been A/B tested and, thus, has been 'proven' to be great business practice.
I’d happily trigger their exit intent handler and juice their “this feature is a total game-changer for our business!” reporting.