Well the answer follows as a roadmap:
- Atom module presents the features of Atom syndicating protocol and it seems like a good place to start experimenting.
Till this I expect I need a month's time, by which we may even have better solutions to the HTTP PUT / DELETE and gfeed.php issues.
- Support for basic query stuff through the GData module. ( remember the 'q' thing ? )
- Atom has a publishing protocol too, which however is not implemented in Atom module, but is needed in GData. Thus the GData module now needs to grow into supporting updations, insertions, deletions.
- Implementing authentication in GData. I except by this time Google will have done more work on this end and impletemention will be easier.
- Testing as usual.
Again this above block should be a month's work.
- Optimise the module's query part so that it is less time and resource consuming.
- Allow the community to test the mudule and go into a full bug-fixing mode.
At the end of this we should have a full working GData module for Drupal.