Well, RISAFloor now has a "semi-rigid" diaphragm definition. But, that just means that you can set a thickness and material of the diaphragm. The same as you always could in RISA-3D.
The only differences is that now the RISAFloor / RISA-3D combination will automatically mesh your diaphragm and will generate standards wind and seismic loading for it. Those aspects are not available in RISA-3D by itself.