The prologue is that I see two issues working against premades. The first issue is that any one group wanting to queue as a premade must be on the same shard. This severely limits the pool of players available to from a premade group. The second issue is there is no system in place for people to form a full group premade be it across shards or not. The system needs queued premades to create a match.
Addressing the 2nd issue first, I suggest that a "pre-queue" be created by designers. When that pre-queue is full then it, that pre-queue itself, could be queued by the raid leader for a premade match. This effectively eliminates unwilling pugs although pugs could join a pre-queue if they want to. The pre-queue system would need to work across shards.
On to the first issue. The system must have premade groups queued in order to make a match. This is a two part issue. The pre-queue system idea (above) needs to accept queues across shards to increase the number of people who are eligible (or who just want to play with friends). This might mean that the pre-queue itself not be limited to a shard group but be open to all shards.
Now to the 2nd part of that first issue. People have to know that others are looking to populate a pre-queue. An immediate solution, if pre-queues existed, is to use special and advertised (in these forums) TeamSpeak and Mumble servers (both of which can work on player comps if they have sufficient bandwidth and a static IP address) so that others can know that people are trying to form a pre-queue. In the long run, some sort of ingame chat channel for that specific purpose could also be created, but it would have to work cross shard and therefore be limited to what kind of announcements it can make (i.e. no individual talking permitted).
Just something to talk about. I hope people find it worth positive discussion.