was about to suggest this, something like....

with the default being just select similar on this object if its a sub-object selection (and global if its a full object selection), and 'global' doing all objects in scene

A very necessary function, I would say basic. I look forward to its implementation

Super useful, especially for defeaturing tasks in CAE applications.

This is an essential feature, at the object level, at the planes and edges level. By size, area, and order of conjugation.

This feature is a must! I am tired of clicking on it over and over again when making car wheels, etc. :(

would be super useful! In Blender i use it all the time. Please also check screenshot below from blender. Select by similar face angle is also super useful as you can easily select similar sharp edges.