Honestly I think there's too much grinding of teeth here regarding flying both. And from the old guys who struggle to learn new tricks mostly from what I've seen in the sim building.....and maybe they're also the senior ones who stand to gain the most from separating the 330/350 fleets....?!? Just saying....
I had absolutely no problems with the 350 differences course. In my opinion if you're an experienced Airbus pilot you will manage fine flying both. The basic flight management is identical. The 350 just has some xtra functions and systems - nothing that's gonna make you lose control. Technically - systems wise - it's a different beast altogether yes - but seriously - since flight engineers left the flight deck and all that stuff was automated I honestly feel that we have so little control over the systems that it makes no difference. So to sum up. It operates the same. Underlying stuff may be different - and you Have to study a bit more to keep up with that but I don't really see huge safety implications operationally.
Furthermore the 350 has INCREDIBLE redundancy. Safest jet I've ever seen the way it's designed.