One has to distinguish between the system in the U.S. and the system In Israel. In the U.S., where kollel families do not constitute a majority of the religious population and has it’s own sources of income (parents and proffessional working wives)in addition to government largess, the system cam probably continue for another two or three generations.
The above does not address the hashkafic issue of whether or not an open ended commitment to learning without entering the work force is, in fact, the Torah ideal.