Yes, this is the exact article that I am looking at right now and according to this, it should be done in one sweep. (and lose all installed stuff)
But oh well, if it is safer this way, so be it! :-)

>Back then the N9 version of Leste was not receiving as much attention
Yes, you are probably right, I do not have much info, but for example, the archive date of the N9 version is March 2019 and the N900 version is quite fresh, 2021 may... But both archive has the same version of 1.0.
So I do not know.

I am thinking of posting a comment about this.
At least to ask about the situation. The article writer posted that this version did not seem very usable to him. But as far as I know, this is the only alternate os project that is active at the moment.
(And I hear they received additional funds from the EU which is very good...)