Make EVA not be a preprocess field

Just saying, DS + EVA (if it wasn't preprocess) would also be a very nice alternative to views overrides of taxonomy/term/% and the like.

These views overrides tend to have their own performance issues, requiring to load the full view for a simple access check (due to views_arg_load). At least, this was the way it worked, last time I checked.

Actually there are two options
hook_ds_fields_info()
hook_field_extra_fields()

I personally found it easier to use hook_ds_fields_info().
Somehow the extra fields thing did sometimes not work.
On the other hand, extra fields work outside of ds.
(and this is not what EVA does currently, or is it?)

Ok, I think finally I understand better what hook_field_extra_fields() actually does :) It only adds rows to the field UI, but does not really create anything on the rendered entity. This is why I always thought it doesn't work :)

EVA implements hook_entity_view_alter(), to attach the fields to the entity.

The cost is:
a) Time spent to figure out which views displays to attach to the entity. This uses views_get_applicable_views(), which is expensive. Even if the view is not used.
b) Time spent to render the views display. Ok, as I understand, we do actually check for $fields['longname']['visible']. But, if the entity is rendered via ds, using "Region to block", then the rendering was in vain.
c) EVA not showing up with ds_extras "Region to block".

I get the idea that the only cure for (c) is hook_ds_fields_info(). However, this only works with ds-enabled view modes.

For (a), and (b), we could try to do something smart:

Instead of eva_get_views(), we loop through $fields, as returned by field_extra_fields_get_display().
Whenever we find a visible field, we extract view name and display id from the field name, and attach a cheap placeholder to the entity display. That is, a renderable array with a #process or #theme function, and a setting for view name and display id, and anything else we need for the rendering.

The #process or #theme does only get called when the field needs to be rendered. Only then do we load, execute and render the views display. I hope this prevents rendering in case the field sits in a ds "Region to block".

In addition, to solve (c), EVA could implement hook_ds_fields_info() and register the field as a ds field. So we would have a different mechanic to render the thing in ds mode, than in regular field mode.
On the other hand, we don't want the field to show up duplicate in ds field UI. So we need to find a way to remove the regular one.

An alternative to EVA (but only for ds-enabled view modes) is
Views content DS