Just had the usual Merlin offers email through with some Ultegra 10sp Di2 shifters, why can’t they be set to 11sp?

because you’d never upgrade

Because shimano.

I thought I read they could?

Pretty sure they can although the mech cant as it wont swing far enough.

They can be programmed for 11spd. They are just switches after all. The cable pull changed from 6700 to 6800. That said, I’m running the reverse (9000 shifters and 6700 brakes) and the braking is just fine.

I understood that they used to be able to run 10 or 11 speed. The shifter only told the mech to shift up or down. However, shimano ‘updated’ the firmware or software so that 10 speed shifters wouldn’t talk to 11 speed mechs.
🙁

They used to be entirely cross compatible. Then Shimano introduced a new firmware update which meant you had to have 11 speed front and rear mechs to use the shifters on 11 speed. So yes, you can do 11 speed with new mechs, but Shimano could introduce another firmware update which renders them obsolete – as they did with the mechs. I’m not aware they’ve done that yet, but it’s possible given the discounted shifters…