As a hobbyist who mostly take videos in vacations - It seems to me that a perfect camera would be one I can take with me everywhere (so DSLR-size at max, not a C700), and is capable enough to produce content with long-lasting appeal. It should work well for stills and video. If I ever decide to shoot a documentary about a subject I care for - it should also work well for that purpose. I want a jack of all trades.
Now, what is a 'long-lasting appeal' to me?
Photos I took with a 5D Mk2 (and a 1D MK4) about 10 years ago - still look amazing to me. The original RAW files hold enough information to impress me today (as a guy that uses mostly M43 equipment).
Videos I took with my GH1, mostly aren't. The limits of the GH1 were known to me at the time of purchase, but coming from an HV20 - it was still a very good upgrade - and the GH1 has been a great camera for vacations and general usage.
If I can find a camera today, that can do in video (dynamic range and noise-wise) what a FF DSLR could do with stills a good few years ago - I'll be happy. It would be the perfect camera for me, and I will not feel the need to participate in the upgrade-race for a good few years to come. The problem is that I don't believe such a camera (within the limits of a 4K USD budget, and the aforementioned size) exist yet - a Panasonic S1H and a the 6K Blackmagic seems to be candidates (well, the later not really for stills) - but I haven't yet seen enough footage to fully convince me yet.
(and yes, I've been humming to myself the intro to "Camera Conspiracies" YouTube channel while writing this message)