Some discussions in the Eternl Discord:
That they – the Midnight claim portal team – request a special API function to get an unused address from Eternl wouldn’t make a whole lot of sense if they did not intend to use it to make that part automatic.
That does not mean that they actually managed to implement it in the end. They – IOG – have promised a lot that turned out to be quite different – often very underwhelming – in the end.
And it does not mean that that cannot be overridden by an unused address of the user’s choice. I sure hope that they offer that.
I wouldn’t be too sure that they offer a path for that. What is verbatim on https://www.midnight.gd/how-to-get-night is that you have to signData a summary of your claim:
For the average Cardano user, they will surely offer that as a dApp.
It would be possible to also offer something for SPOs where they can download the data and sign them on command line. But haven’t heard if they plan to do that, offer documentation and support for it. Wouldn’t bet on it.
(Problem is: If it only pops up once the portal launches, time is limited. They’d only have 60 days to offer work-arounds.)
Alternative is to import the .skey files to Eternl. Then, a dApp connection can be done with it. But still no unused address for obvious reasons. So, still the hope that they just offer a manual override.