A big lens announcement would be a 1200F5.6 lens...... But I'll settle for an updated 400F5.6, it would be a lot easier to carry.
For such a 'big 'ens' I'd expect the announcement to be 'small', aimed mostly at professionals that might actually use this niche product.
If it is a significant lens, I'd think it is something coveted by many photographers, such as the 100-400 shown at the start of this thread, or maybe a new 50L. Somehow I think a 35L is not significant enough.
So based on the original info I'd say if anything is anounced, it's an 'L' telezoom, normal prime or quite possibly a WA zoom with a new range.