I don't see the point of rewriting ReAction, Installer and all the rest from scratch when I already have them...
But you already made the point...

If you want it open source, that's the only way that is going to work. Is this really so hard to understand?
I don't really have time to do that and write applications too.
But you expect others that they make their work available for free and invest this time? How charming...
Even if I did, there's no reason to think they would get put into AROS, as it seems fairly clear that they are MUI zealots, standards be damned.
Drawback of open source. You cannot have an "open source that works only how you want it to work". That's a closed source model.
Plus even a complete reimplementation would still be just a reimplementation, not the real thing.
What's unreal about a re-implementation?
Why would anyone want to do unpaid work on a piece of closed-source commercial software which is still being sold!?
Why would you want to do unpaid work on closed-source commercial software that runs on obsolete hardware? This is neither logical.
Look, it's really all a matter of perspective. You should understand that your demands are not even self-consistent. Step back, think a while about your priorities and what your goals are, pick your decision within the available constraints.
I'm not demanding anything, what am I expecting to get for free? I have pointed out some of what's missing from AROS which keeps me on OS3.9, from a user perspective. I'm not demanding anyone else implement this, it seems obvious after 15 years that it won't be implemented. They're wondering why people don't want to use AROS, and I'm giving them the answer. As simple as that.
But then it's your turn to change it. Why don't you implement the missing bits and pieces, after all? If you want a challenge, it's right in front of you. You refuse to contribute because it's not complete enough to compete with 3.9? With that logic, nothing will ever get done because nothing will ever become complete, it's a completely circular argument. It's actually not different with commercial software. At some point, you need to get your arse up and start, no matter how incomplete it is.
Surely I have the right to say why I don't use something without having to volunteer years of unpaid labour on a piece of software I don't even like. By that logic, if I say why I don't like Windows, I have to go do unpaid work for Microsoft.
No, by that logic you can either buy another product, or contribute to a product that allows contribution. You can buy Apple, you can contribute to Linux. Same difference. If you want to *contribute* to Windows, well, that's going to be harder - seek employment at Microsoft. But it is no option that Microsoft will release the windows source-code for free, to allow you playing with it. Won't happen. It's their source, they define the rules. You don't like the rules? Pick another product. Your choice. Quite the same here: You don't like Os 4 as a product? Pick another one. The owner does not allow open source? Ok, their product, their rules. Want other rules? Pick another product. You have all the options right in front of your table, you only have to make your pick.
More on topic, I can confirm the incompatibility of Birdie with the new layers.library. Do you know which of the two components is to blame?
Birdie goes into the internals of layers, and these had to change slightly - the external API works the same, though. Layers pools now many of its structures, to avoid the "fragmentation bomb" older versions threw at the system for their "slice and dice" implementation. As soon as a program modifies internal layer structures by bypassing layers, this is going to be a problem.
As far as Birdie is concerned: I don't have a contact to its author. Do you? Does anyone in the community have?
Essentially, Birdie provides a functionality that would require integration into intuition - not layers, as layers doesn't even draw anything, it only clears out layers optionally by a backfill-hook. Layer is rather the "victim" here as it provides some information on when intuition performs its activity.
One way or another, I don't think that Birdie is an essential miss. It's only eyecandy.