I would suggest that the ULBs requirements are:
Detection Range At least 25 nautical miles in open ocean
Battery Life At least 6 months, possibly by reducing number of pulses and using smart transponder that does not go into regular short location signals until it receives a search request sonar signal
Encoded Location Signals The signals from the ULBs should be encoded with airframe ID, their position (last GPS position of the aircraft) and their depth in the water.
Current Range seems ~2.5NM, 30days.
So you asking for something that lasts 6times as long (maybe a bit less due being "smart"), and is 1000x as powerful? So needing say battery capacity 2000x current kit?
That is a "major" change, and bearing in mind the 'g' / depth / other strict requirements I suspect unrealistic. NB just stuffing big batteries into autonomous kit is hardly flavour of the month right now (787 LHR fire).
Bear in mind these things do not directly save any lives, and assuming they find the Air Asia DFDR / CVR soon, just save some search effort.