We don't need one "big bang" change, we can go giving little steps to replace PM, SOM, CPI, etc... file by file if it is necessary.
That is a dramatic wrong wording IMHO. It does not need 'little' steps but giant leaps to replace only one of these parts with open source alternatives that have nearly the quality level we are used to and which OS/2 - eCS users are expect before the even want to try out your replacement component.
You will not find the community which is willing to test and bug fix any OS/2 replacement component when it sucks like the first Linux versions or the examples you've stated above. None of the serious OS/2 developers will only waste a minute looking into messy code as Sergey describes above. It is a big difference between tinkering with some code snippets and coding medium sized quality level applications (read usable replacement parts).
Most probably you will not
...need right now is someone with the interest of talking a look under the hood...
as this was done hundred of times before. The conclusion was always the same - it would need way to huge investment and man power to only replace one of them for our community. Even when we were 10 times as much and 10 times as rich as we are your dreams are so much out of reach you probably can't even imagine. Sorry I've to say that
Think about why only very few people even test the os4 kernel. This is an example of a piece of software which is not that bad at all. In fact it works remarkable well on a lot a machines. But beside the legal concerns which I don't want to discuss here it has a few limitations. This few limitations (documentation, trace support, incompatible with ACPI) prevents usage and testing by a wider audience. Why do you think a lot of people want to play with replacement components which for sure will have a lot more bugs and incompatibilities when you do not even find the testers for much more advanced projects? Why do you think a broader audience is willing and qualified to develop, document, make install packages and test a replacement component when we do not even have the man power to support running projects like AOO, Firefox, Seamonkey, Apache, all the ported QT apps..... ?