In most other art programs, if you hold certain keys with the lasso tool selected you can modify the behavior of it.

Reproducible: Always

Steps to Reproduce:
1.select lasso tool
2.press shift
3.make selection with shift pressed

Actual Results:  
nothing special happened.

Expected Results:  
the newly selected area should be added to the existing selected area

Shift would be add to selection
Ctrl would be delete from selection
if possible, Ctrl+Shift would be intersect
and if no key is pressed, then the normal behavior should be simply "replace".

I know you can do that via the tool option menu but it'd be very intuitive and fast to have these shortcuts.