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 | EF: SY14/2.8, V20/3.5, 28/2.8 IS, Ʃ35/1.4, 50/1.8, 50/1.8 STM, Ʃ50/1.4 EX, 100/2.8L IS Macro, 16-35/4L IS, 24-105/4L IS, 70-200/2.8L IS II, 1.4x II, 2.0x III, T28-300 VC PZD, 70-300L IS, Ʃ150-600 OS HSM S | E: SY12/2, 35/1.8 OSS, 16-70 ZA OSS, 55-210 OSS, SY300/6.3 ED UMC