Just look at the bugreport that he references, and then at the related bugreports.
They are all closed as not fixable and reference to the packages wiki for more explanation.
That is for a reason :-)
Hmm. It was me that dug out and referenced the bug report. I didn't see any mention that the bug was unfixable, instead I saw reasonable caution and a patch that appears to work. Of the three related bugs, two of them were closed out as resolved, and only one left open.
I've now read through the related bugs (and a few more), and on one that was left open indeed on one of them Vincent raises the same concerns you do here. And phew, reading
http://wiki.lazarus.freepascal.org/packages makes my head hurt.
So, how to proceed? I don't have expectations that Lazarus is perfect, and I'm impressed that the LCL can be accessed at all through DLLs. I'm guessing that you're just raising the concerns that people who proceed down this path should simply be aware that they may encounter unfixable problems.
UPDATE: Been thinking this one over... Or are you saying that the people should not attempt this at all?