I don't understand about RC lack of functionnality for such system ?

RC currently allow all data export : R syntax and R data for example. But if you hace a system that can work with triple-s : you have a plugin. No need more RC system in my opinion
(and you can export as json too : used by a lot of system).

Seems to be the only approach for real world scenarios. I'm still waiting to see a complete dashboard via remote API. The restrictions seems to be too high for that. 

@jelo, after having developed a few more dozen reporting dashboards we are still using the approach of directly loading the data from the Limesurvey database. For large surveys the performance is far better. Especially if you need to load additional data like question attribute details for questions, the API is not a good solution.
We have come up with our own kind of reporting framework which we are using for custom Limesurvey dashboards . For each question type a certain underlying chart type is defined which can be adjusted if needed. Such reporting plugins also allow marking special questions to be available as data filters (e.g. gender, age range, ...). So overall, one can create really nice reports this way. I am attaching some screenshots.