I would guess this discussion will eventually turn to an extended derailleur hanger like the Wolf Tooth RoadLink.

I have them on my mountain bikes to run up to a 40t, within rear derailleur capacity.

There are mixed opinions, and I haven’t used one on a road bike, but I think they do as advertised at the expense of some shifting performance at the high end. I have no idea if there are issues with Di2.

It all depends on the priorities and what compromises someone is willing to accept.

John