When I first saw this thread, I honestly LAUGHED!!! The idea of the PS4 even coming close to Wii sales numbers, sounded ludicrous!
...but then I decided to try and take the topic serious for a few minutes and simply look at historical numbers, just to see how out in right field the idea was - and while history is definitely not a GUARANTEE of future trends, it's certainly a worthwhile indicator. So, hang with me on this for a minute or two, and see if my logic holds.
I think we can all agree that MS & Sony are marketing (and generally sold) to the same type of players - so, when you look at the past combined sales of those consoles, you have:
PS2/XBox - Approximately 180 million (vast majority went to PS2, but it released well before XBox)
PS3/X360 - Approximately 175 million (nearly identical numbers for both consoles)
PS4/XBOne - About 95 million so far (PS4 is currently outselling XBOne 2:1)
If we ASSume that the PS4/XBone generation will eventually hit that same 175-180 million mark combined, that would mean another 80 million or so PS4/XBOnes will be sold by the time the next generation starts. If the PS4 continues its 2:1 sales ratio, then that would put that 80 million split at (about) 50 to 25 million (PS4 to XBOne, respectively) - putting the final sales for both consoles at: PS4-63+50=113 million vs. XBOne 31+25=56 million.
PS4 edges out the Wii ever so slightly: 113 to 101 million.
Now, obviously my entire post is LOADED with ASSumptions and wild speculation - but even still, at least I've attempted to back up my approximated claims with some historical trends... ...and by doing so, it makes the OP a little more believable and not something I could just laugh off, as I initially did.
...just a couple of pennies from me. :)