After what happen to SCV & Lost Swords, chances if SCVI wasn't successful BN may not give SC another chance. TN making a weapon based fighter would be an interesting idea, it would be a perfect chance to cater the "cool crowd" that wasn't a fan of DOA content.
Yeah, I can imagine SC6 being the last game if it doesn't meet expectations. The last good soul calibur was the third one in my opinion. Four felt a bit slow and heavy when it comes to character movements, and V sort of had a subpar story with the new characters not being liked too much (talking mainly about Patroklos and Pyrrha), also, game died very fast for some reason.
The last good all-round SoulCalibur was actually SCII. SCIII's balance was horrendous despite having the most offline content. SCV died off quickly because some moron at Namco thought it would be a good idea to remove a lot of fan favourite characters and replace them with lame anime tropes. So what's SCVI's strategy? Bring back the characters they stupidly removed in the first place.
Just guarding ruined SCV in my opinion. Allowing players to just guard safe moves and punishing them for playing safe made me want to claw my eyes out. Thankfully, they changed the way just guarding works in SCVI. But I'm one of the few that did enjoy SCV.
One of My favorite things to do in SCV is spending time on customization and recreating characters & costumes from Soul Edge/Soul Blade (Arcade & PS1).