The idea behind Neo900 is not death, actually it is better everyday.
Making 4G and CPU/Memory upgrade board for old phones to use Maemo Leste is upgraded idea

But why think only N900 to upgrade, maybe is it better design small enough "compute"-part and separate IO-part for different phones, so ports are right places..but because there is so less room for two PCB, have to make one PCB (and it is cheaper and more easy to fit). But not have to design from start for every phone.

And maybe it is better think old cool symbian devices like 7710/C6/N97/E6/E7 or old Maemo tablets 770/N800/N810, they have room and not have phone/4G-functionality at all already although they mic&speaker, so upgrade would be big change for them.

Also not forget old comminicators, touch screen is not so important, when you have keyboard/"mouse" like with 9300/9500 or E90.

Maybe there is some not Nokia devices good for upgrade for Maemo Leste?

What you think?

CPU and RAM are the main problems with all the phones you have listed

Also, https://neo900.org/ ... it's no easy task

That's why they are good for CPU and RAM upgraded board.

It is not easy, but is not impossible. It is actually more easy than when they try. Now there is Maemo Leste and you can choose components more freely.

I just thinking would it be Raspberry Pi compute module version with self made I/O-board in some of those devices?

I hope I am wrong, but I don't think you gave yourself any time to understand the link I gave you

Actually I have readed all this:
https://neo900.org/resources
somewhere 2018 and that time I though..who can make it to work with software..and now software side can take new leap, because Maemo Leste. That is why hardware can also make new leap, because it doesn't need to be compatible to original model.

Neo900 might be death..only usefull information these days might be measurements of N900 and idea about spaceframe to give more room to new hardware. But as I said better think NeoN810 or Neo9500 than Neo900.

But isn’t the hardware completely obsolete today?
Also Leste is still in pre alpha and phone for example still doesn’t work with n900 at least. Also with 2G/3G going extinct soon ( already in many places), it probably never will.
Besides that, since Leste is still years away from being ready and can’t even completely take advantage of everything with really old devices, what is the point of having a modern device with modern specs?
Just curious of course. I would definitely like to see something modern, good and actually usable, but I gave up on the idea years ago.

How Leste is still years away?

Is there a fully functional open beta that I missed?

No. Only CPU,RAM and modem if installing modern big linux. That is why I said about upgrade board.

I think reason is that we don't have complete documentation for old hardware. If we have upgrade board with 4G or 5G modem that we have documentation.

I still use the N900 as my main phone and the hardware works fine. 3G and even 2.5G are both still supported where I live and there are no signs of it disappearing any time soon where I live, USB Type-B Micro cables are still widely available, Televisions still use infrared, etc. So for me the hardware is as usable as it ever was.

The hardware is outclassed in speed by modern devices but that does not make it any less usable than it was in the past. Personally I would be willing to pay a lot for an upgrade like the Neo900. The N900 still has nice features that modern phones typically do not have, like a keyboard, infrared, larger part free software, etc.

Personally I would pay big for a Neo900, even though the hardware is old. It is better than what I am using and loving right now. I find it really unfortunate that the project did not succeed.