ULB
There has been some discussion on here about making the ULB an 'active' system where it scans for an 'initiation' signal from searchers and then replies, therefore extending battery life.
What can be done much more simply is to double the time intervals between 'pings' which will roughly double the battery life. This increased 'capacity' could alternatively be used to power a frequency lower than 37.5KHz for the same 30 days but with an extended range or indeed a combination of the two things depending on what SAR believe would be more useful.
Personally I believe an extended range would be more beneficial than greater endurance, especially in situations like we have with MH370 where we don't have an exact location. In fact I would suggest that the frequency of pings are reduced from once per second to an interval which will provide enough power to support a frequency that allows the range to extend above the surface of the sea in most areas.
Then a ULB search could be done from the surface or the air without having to rely on the much slower towed array.