I've had no problems doing it, without any status at all. You just have to call.

Sorry for reviving this thread... I am having a trip to SFO recently in PEY so I want to check the loadings of the flight (to evaluate op-up chances). However, upon checking the PEY/Y seat map on EF, I have a few interesting discoveries:
1. PEY zeroed out in W/R/E fare classes, but seat maps shows 10+ open seats (not really surprising since many people don't select seats in advance);
2. EY seats seems to be blocked from row 42 onwards in the first section (on the 77H) and 65 onwards in the second section, with the exception of row 71 and 72, which is more than half of the EY cabin. And this seat blocking seems to apply for all flights (even wide open flights in April 2018)

So just out of curiosity, what do those blocked seats represent? Who have access to those seats? They are towards the back of the cabin, so I don't think they are reserved for elites?

Probably reserved for airport control so when groups check in they are able to arrange seating together without single travellers having broken up the whole grid into non-contiguous blocks.

If an elite calls in and really wants one of these blocked seats, they will release it.

If I see a blocked seat suddenly become occupied (on EF), is that a sign of an elite calling in to get it?

When an elite books a flight, he/she can be assigned a seat anyway without calling. Some influential TAs can also get seats for clients.

moved for a baby?
 

I also got the warning when I called to have seats opened. How often does this happen?

In F and J? Possible, but rare. More likely to happen in Y or PEY.

PEY - I'm not sure. As you say it could be people just not selecting seats yet.
Y - seat groups will be blocked for tour group bookings so they can all sit together, usually at the rear of a cabin section. This is a good thing.

It is extremely unlikely for a 77W or any widebody to require seat blocks for weight/balance issues.

Since nobody can say with certainty, and it's all speculation, I'll posit that the block represent a few things.

1) The blocks for the things mentioned above, such as bassinet, DM adjacent seat blocks, groups, crew rest, and so on.

2) Reservations that do not have seat assignments. Basically a placeholder.

I see some claim that #2 is not true because the blocks disappear T-48. But why would that disprove the theory? That is the time you start OLCI, and have an opportunity to pay for your seat assignment, right? (At least that is the way it works on other airlines. I always select the seat when making the reservation CX.)

When large section of seats blocked, especially towards back, chances are that they were for groups.and normally Cx wouldn’t release them to you

I assume, Weight & Balans. When the aircraft is far from full, you don't want the payload weight to end up concentrated in the back, since, that'll require major re-seatings, to be able to stay within W&B limits.