i don't know about this with passions, (i am 'grasshopper' here, and they are teaching me ) but yes, i root many plants and they absolutely flower in order to survive. but from reading through these board exchanges, i get the impression that many passionflowers (from seed) do not flower. I hope the more experienced see your post and can better answer your question. i would like to know this as well:)
Nicci

I'm no expert but have found that my plants do better in large containers or better yet inground. It's just a pain to lift the non hardy varieties in the fall. I've heard that some don't flower from seed but haven't found that to be a problem with the plants I've started though some have taken a couple years to reach blooming size.

I understand that many hybrid crosses won't flower from seed. Occasionally, a pure strain species plant might not flower from seed, but these are much less common.

I have read a site about someone seeing a passion fruit vine growing by an paved parking lot with hardly any soil or room space and surprisingly thriving with lots of flowers and fruit set!!! I personally believe that it benefits the vine to shorten root space for a year and then transplant the vine once all fruit has dropped and there are no more flowering. Hope this was of any help.

Daniel