We need to be fully compliant with LAS 1.4 with all point record formats since many vendors provide their lidar data with all of the point record formats available in LAS version 1.4. Full waveform support is not required at this time (although I don't think anyone would object), but full access to the data in LAS version 1.4, e.g., full range of class codes and record formats, would benefit the community of users of lidar data and ArcGIS's LAS Dataset.
Currently, from the ArcGIS resource center:
"ArcGIS supports LAS versions 1.0, 1.1, 1.2, and 1.3. The waveform information that is available when using LAS version 1.3 is not supported. Additionally, LAS version 1.4 files that are 1.3 compliant, containing point record formats 0 through 5, are supported. LAS version 1.4 files containing point record formats 6 through 10 are not supported. "