> Add missing remappings for Ido mode
> Among others, add a remapping for C-x 4 d, cf. Bug#26360.
This reduces the effect of ido-everywhere to the point where I wonder if
there's any point keeping it.
ido-mode and ido-everywhere are very different: ido-everywhere only changes the completion function, ido-mode has semantic knowledge about the commands. For example, C-x 4 f C-d visits the directory in another window; that is impossible with ido-everywhere. On the other hand, ido-everywhere works for other commands not explicitly covered as well.
Alternatively, wouldn't it be preferable to not use this patch and
enable ido-everywhere by default instead?
No, as described above, they are very different.
What are the tradeoffs?
The installed patch solves a concrete problem now. Converging ido-mode and ido-everywhere (and ido-ubiquitous, ibuffer, iswitchb, ...) is desirable, but orders of magnitude more work, therefore infeasible.