First - I agreed we can keep both. With versions it won't break anything. If the user wants to continue using this, they can specify legacycontinue parameter in addition to version. Its a win win - the simpler users will use the more direct approach without much thought, the more advanced users, in an unlikely case they find use for it - will use the legacycontinue. The important thing is that default is easy, not hard.

Second: 

Please look closely again at my description of different use cases and their server load.  Your examples are absolutely no different -- It does not matter if the properties on the page have many links or few links - the case of pltitles=Foo or no-link categories  - you still will want to look at either 80% of the page titles in one block - in which case you execute all the subquery continues, or you need just one or two page titles per block, in which case you would have saved server resources a lot by filtering them first and than asking the server with a pageid list. When I designed generator, I assumed that ALL needed properties will be returned at once, without any continuations. With the addition of the prop continue, this model breaks down and becomes very inefficient.