It was removed because some people were complaining that materials were not properly converted sometimes - due to usage of the selection modes. What people did not understand is that they only converted materials but no maps. That was on purpose and that's why they were marked as "debug" modes, to test how conversion works. If those modes also converted maps it would either convert maps from other unselected materials or simply break all instancing between other materials, both is bad and undesired under normal circumstances (more ram, slower, etc). So, since it didn't make much sense to use those modes as a normal user and to avoid confusion, I removed the debug modes.
How long does it take to convert a scene? It shouldn't take more than a couple of seconds, even with hundreds of materials. If not it might be a bug and I'd like to investigate this issue further.