The select_linked functionality allows many great selection possibilities. With some use-cases this sort of selection can become quite fundamental.
Both currently available operators have drawbacks in terms of workflow, which get quickly apparent in such situations.
Select Linked:
-works on the context thus requires two steps for every patch selection
-SET/SUB selection of a patch require even three steps
Select Linked Pick:
-rather awkward when to perform selection with a keyboard key while aiming your cursor
-SUB selection of a patch requires two steps
-SET selection of a patch requires three steps
Solution
This patch exposes the Select Linked Pick operator as an active tool as part of the selection tool group in Edit Mode.
{F8269051}
In order to keep consistency with other selection tools this patch also replaces the operator's deselect property with a mode enum. Like other selection tools the mode enum is exposed in the tool header and mapped to the corresponding modifier keys.
{F8269054}
Addressing the problem like that has still some con's:
-box/circle/lasso tools can't be used to select regions
-Inconscient with UVEditor island selection
This problem could also be addressed differently. From UI perspective it would be obvious to expose this functionality as a selection mode similar to the UV Editor island selection mode. However that would probably not be straight forward to design and implement. Also it wouldn't really mirror the implementation as a linked region isn't a real element of a mesh.
Open questions:
-would it be better as a selection mode?
-should AND/XOR selection modes also be supported?
-should the Select Linked operator be updated to include the mode enum?
-should the (L) shortcut be removed / replaced?
-LINKED_SELECT_DEFAULT_HACK is in charge of some glitches, the behavior seems ok without the hack, is it still needed?
Additional discussion on this topic:
https://devtalk.blender.org/t/in-the-sub-object-levels-there-should-be-an-element-level/9396