But my suggestion is that we start to compile a catalog
of such problems, rather than submitting bug reports.
Where is a good place to start?

Could it be this very mailing list, because AFAIK there is no active page for discussing about intersource matters.
Another place could be Gdansk: probably several of us are willing to go to Wikimania,
an I consider it a crucial occasion to meet, discuss and understand each other.
Wikisources are many, very different and extremely complicated, but with great, huge potential.
Best thing we can do is to see each other in the eyes and start creating a proper intersource community,
sharing experiences, competences and ideas.
I'll be there, hope you'll be too. Maybe we can arrange a meeting.