For those who would be interested in a complete working example to fill EXT 4.1 GRID with JSON data provided by IBM Lotus Domino, here is a small example I've cooked for you.
This is more or less an update of this initial post.
You can find my example here :
As it doesn't use any agents or converters of any kind to preprocess data, the grids are built at lightspeed.
I've tested it on a database of 45Gb, with 450 000 docs with scan attachments, and there are no problems at all. Just have to be sure your view indexes are up to date.
Domino remains an impressive server.
Have a nice day.