4A+4Lz+4Lz could hypothetically be executed according to the definition of a jump combination, since no change of foot or edge would be required between the jumps (just a change of direction for the middle quad lutz ). OK, so even doing that combination with singles would be hard enough (and really cool) so it's not likely to happen ever but would be legal under the current rules in the Junior and Senior Men and Ladies Free Skate.
In the current code, the base value for the combination is:
4A+4Lz+4Lz = 15.0+13.6+13.6 = 42.2
If done in the second half, this gets multiplied by 1.1 before applying the GOE:
42.2 * 1.1 = 46.42
The GOE addition to the base value for a +3 GOE for a jump element containing a quad axel is 3.6 (the most of any singles jump or element). So if the combination got all +3 GOEs (or all counting judges gave it a +3), then the final score for the element would be 46.42+3.6 = 50.02.
I'm in the process of doing more nerdy calculations also.