The Silmarillon is not as accessible as the LotR or the Hobbit. That's partly because Tolkien never finished telling the story himself, of course, but also because there are really no characters like the Hobbits to mediate the readers' relationship to the high fantasy. Human beings don't even come into the story until about a third of the way through. Even then, they are of the heroic variety for the most part.
It's more like reading actual myths or arthurian romance in a condensed form.
It would be a challenge to adapt, but not impossible. It could also end up being extremely lucrative. I think you'd end up with the following basic stories:
Feonor and the Silmarils
Beren and Luthien
The Children of Hurin
The Fall of Numenor
The first movie would probably be the trickiest, honestly, as it would have to establish the whole mythology, and would probably have to introduce humanity once the Elves arrive on Middle Earth in pursuit of Morgoth. Some adjustments would have to be made with the chronology here, but nothing out of hand.
Beren and Luthien, along with the Children of Hurin, are the two sections that most easily lend themselves to stand alone stories. As somebody mentioned above, you could start the Beren and Luthien movie with the Fall of Fingolfin, which would be EPIC. This movie would also introduce Sauron.
Similarly, you could start the Children of Hurin with the last stand of the men of Dor-lomin (sp?), equally epic. Mostly it would focus on Turin. Lots of good characters here, including Beleg and Mablung.
The story of Earendil would start with the Fall of Gondolin and end with the defeat of Morgoth. The trickiest aspect would really be the first movie. It would have to cover a lot of ground, and that story has the least obvious hook. For that reason, another possibility would be to start in medias res
with Beren and Luthien, and continue from there. This story is rich and complex enough that it could actually be two movies, same with most of the other stories mentioned above. It has everything, really. Strong male and female leads, epic adventure, romance. Less detail in the actual text than with the LotR, so plenty of flexibility for the director.
The budgets for these movies would be off the charts, though.
I'm speaking as somebody who doesn't like the Jackson films much, by the way. But the reality is, somebody is thinking about these scripts as we speak. You could easily make six or seven huge movies with this material.