Yeah, that is my understanding as well. Given how conservative the company is, I would adjust my expectations accordingly and not expect a complete revamp of their line-up.
I would expect that Tiagra gains its 11th cog or 11-speed 105 mechanical is pushed downmarket (or that 105 gets a cosmetic redesign and is rebadged). I would not expect to get mechanical 12-speed groupsets, though, that’d surprise me.
Even if I am wrong, then the revamp would still be straightforward: Ultegra mechanical gets cranks, cassette, etc. from Ultegra Di2. But I wouldn’t expect anything “revolutionary.”
Certainly seen the rumors of 105 12 mechanical and GRX 12. The rumors I have seen in just a couple of places seem to suggest something more revolutionary rather than evolutionary, but maybe I am just reading into it. Maybe that is all that it is.
What would be awesome is if they move GRX 12 to a true off-road group, and make mechanical GRX shifters that were compatible with their mtb rear derailleurs which would open up all kinds of drivetrain possibilities. Would be good if they have Di2 versions as well and release 12 speed electronic mtb groups.
That seems to be the plan, and I think this is what Shimano will most likely release: they already sell these chainring options (on 11-speed groupsets) and last time they did not release any new GRX-specific cassettes, but just took what they already had on the road side (2x) or 11-speed mountain bike side (1x).
I reckon Shimano doesn’t think it is worth it. SRAM can use its groupsets on all bikes whereas Shimano has bifurcated its product line.
IMHO it’d be nicer marketing-wise if they simply erased the distinction and simply made e. g. a GRX version of, say, their Ultegra Di2 rear derailleur that only differs from the regular one by having a clutch. Ditto for shift/brake levers. I have heard from quite a few roadies that they prefer the shape and additional leverage of GRX rear derailleurs. By having them completely interoperable, someone with an aero road bike and 0 gravel ambitions could opt for Ultegra GRX shift/brake levers simply because they prefer it, while having matching optics.
Good point. SRAM has a Wide and a regular front derailleur, too. But it is still e. g. Force, and I think you can use a “gravel crank” with a standard (non-WIDE) rear derailleur, too. So I reckon Shimano could have followed suit.
Perhaps Shimano could have even designed a bracket or so to accommodate the differences (in height and chain line).
Isn’t that a design choice, though? Either Shimano could have split the difference or used e. g. a spacer or a setting for the front mech. (Although that doesn’t seem likely given Shimano’s history to e. g. make chain rings specific to a product line, my XTR M9000 cranks won’t accept XT chainrings, for example.)