The line between safeties and corners is getting more and more blurred. You are getting a lot of safeties who have the quickness and coverage skills to play corner, and it seems that the big, linebacker type safeties are becoming more obselete.
If we are having this much trouble figuring out where AThomas, Vrabel, Wilson and Meriweather will be playing, ya think opposing quarterbacks might have a few difficulties figuring it out as well? If everyone can stay healthy, pre-snap reads are going to be less than helpful. I think you will see lots of movement and covert formations before the snap. Are they blitzing? Who is blitzing? Are they in a zone? Who is the safety? If disguised well enough, the entire offense will be guessing.
As for linebacker and corner/safety acquisitions next year, look for this trend to continue. To get a 4-6 year commitment (FA or high draft pick), you better be able to blitz, cover and adjust to multiple responsibilities on the fly. The NFL is a quarterback/passing league. Nickelbacks are almost considered starters and "2-down" run stuffers have become specialist (short yardage/goal line).
We all seem to be anxious to put players in neat little boxes (LOLB, SILB, WILB, ROLB, SS, FS, LCB, RCB) that define their strengths and responsibilities, but who says it has to be that way? In fact, these very specific designations only serve to help the opposing offense. Hard to identify if the SS is in the box if you don't know who that is...or even if there is someone doing that "job" on the field.
I think Meriweather is going to be a fine addition. If his mental abilities can match his physical tools, this defensive scheme (and the other skilled players executing it) could make him a weapon.