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.
5D3, 5D2, Sony α6000, G16 | SY14 f/2.8, Ʃ20 f/1.8, 24 f/2.8, 35 f/2, Ʃ35 f/1.4A, 50 f/1.8 I, Ʃ50 f/1.4 EX, 100L Macro, 17-40L, 24-105L, 70-200 f/2.8L IS II, 1.4x II, 2.0x III, 70-300L | E-mount: SY12 f/2, 30 f/2.8 EX DN, 16-70 ZA OSS, 55-210 OSS, Metabones SB | FT-QL, AE-1P | FD(n) & FL lenses