This topic deserves a full keyboard. I currently have only my phone, so here's my slimmed-down response.
When you're in the pod, all stimulus comes via your implants and is already enhanced with sound and such to make it easier for pilots to apprehend. I think this should mean you have enormous power to customize how you perceive things, much as we can choose which skin we apply to this forum, but much moreso. Combat as squashing ants in a playground, a cliched FPS or a game where you have to catch cartoon ponies and tickle them until they pop into rainbow-coloured bubbles are all possible. Setting your social overview to show only people you know/like. Interpreting virtual environments so you see your companions as cats, or floating eyes, or pieces of antique furniture.
I've played - briefly - in a virtual channel where one of the fun things was inventing virtual costumes or whole new avatars (ask Gottii about his God of War costume) and where one of the pranks was to set someone else's default avatar to be something quite unlike what they thought they were projecting. Much fun.
I've played that all sensation and experience is stored - or at least temporarily buffered - by the implants (think combat and chat logs, but with feeling) and those can be played back or even shared (think William Gibson's short stories and the new entertainment industries there). This got more complex, since it implies or suggests a number of things which go far enough beyond canon that they'd cause a fork in our realities. We stepped back from this after a neurological-specialist expressed admiration at our inventiveness but concern about the consequences... Which could include some of the issues you raise. (Mata and Gottii have both blogged about that, but it's probably a bit cryptic if you don't already know what they're on about.)
As for merging the datastreams directly... I think any accidental overlap - if such a thing were possible, and we're still waiting for the ruling about cloning which would tell us whether the data-squirt or quantum entangling model is "correct" - I think you'd be more likely to get nasty interference patterns and garbage. If this grows as an art and a science you might, in time, get conscious choices to "become" parts of other people, or edit your own memories (Eternal Sunshine...). Lots of potential for fiction or "performance" role-play. Frustrating as anything for participative role-play.