I'll list here our current situation, TDW and Zedi can comment if you have something to correct:
Good things 
- High quality, functional ships imported from SH 4 with all maps and textures working
- Illumination, sun affects ships lighting
- Ships take damage from Deck Gun and Torpedoes
- Damage graphics (holes and internal structure) show when looked underwater
- Possibility to add SH 5 wakes
- Animated, fully working Sh 5 crew
- Possibility to add SH 5 or Sh 4 guns and instruments to ships
- Basic importing is fast
Bad things 
- Ships don't cast shadows
- Ships don't reflect through water when looked above waterline
- Illumination anomaly (wrong side of the ship illuminated) when camera is really close to ships
- Damage graphics (holes and internal structure) don't show when looked above waterline
- Guns are rendered completely black, Sh 4 guns show textures only when camera is really close to ships
- Caustics show only on one side (SH 4 feature), Sh 5 caustics don't seem to work
Uncertain things (haven't been tested yet) 
- Flooding modelling is unfinished
- Some ships seem to bounce and roll too much when travelling