As it is now, you can only do one daily to get 2 sourcestones from a raid quest. Since not everybody can join a raid rift i suggest that you can chose between sourcestones or plaques when you do some expert instance using the LFG.

Since in this way it could end with people doing too many dailies and getting too many sourcestones, i think
it would be a good compromise to give this option only once a day for t1 and t2 (2+2), or just 2 from the raid daily + 2 from another instance. In total you could only get 4 sourcestones.

Raid rifts are funnier and faster but not everybody can join them, while the lfg doesn't seem to be used that much and in particular for t1 instances, that are mostly avoided.