That was about CivRev, a bad mechanic that wasn't fixed and people abused it by destroying an enemies capital (via nukes, or if a barb did it) to disallow conquest victory, then you can work on your other kind of victory unimpeeded.
In Civ Rev you Couldn't destroy an enemy's capital with a nuke (plus there was only one nuke per game)
As far as how Capitals will work, we won't know for sure till we get to play and test it out.
But as far as we have seen, after your capital is conquered you can build another one, (for trade route's, social policy bonuses and anything related to capitals) accept we assume your capital is still considered dead in terms of domination victory (although, they may simply of not been rebuilt, but if thats the case then this domination capital victory would be more like a normal conquest victory), as we saw a screen shot of capitals having been lost on the "win conditions screen" this also suggests you don't actually need to control all capitals to win the game, merely be the only Civ who still has control of his original Capital, this unfortunately will mean If you have conquered the entire globe and control 17 of the Starting Capitals and leave your Original Capital ungaured, that last insignificant Civ who you have ignored maybe because he was your friend, can send an army and conquer your Original Capital and then he would be the only Civ with its Original Capital, and he would win. Now while I really dont like the fact that you can beat a warmongerer and claim domination even if you did none of the work, I guess this will make people protect their Original Capitals a bit more, as you will need to control it to stop anyone else winning Domination, and definitely make sure you protect it if your aim'ing for that Win yourself.
Thats just my assumption on data known, it could work in a completely illogical manner, so we will need to wait to know how it all works.
Its true it Could work in an illogical manner.
However, Likely that will be patched, require you to control all 'capitals' in the game.
Variations include
1. "Hunt the Capital".. ie civs can rebuild their Capital with Certain restrictions (say must be pop 10 or it takes 10 turns, etc.) and the military Victory goes to whoever has the last existing Capital.
2. "Beheaded" Lose your Capital, lose the game (your cities are eliminated or become independent/Vassal)
3. "Have Your Original Capital" (as described)
4. "Secondary Capital" that can be rebuilt functions for Some other purposes but not related to Military Victory
#1 I Could see if the requirements were serious enough (say If you have a city over Size 15+ your largest city will start becoming the capital (takes 20 turns))
#2+#3 seem like they would be unfun/illogical and probably patched.
#4 seems possible, but potentially confusing to those who don't understand.
I could see "Require Complete Kills" as an option (where every enemy city must be eliminated instead of just the capital)... but that would almost be equivalent to eliminating "Military Victory".. since if every enemy civ is eliminated, you Will win (by Time, Tech, Culture, or Diplomacy)... unless Barbs/City states wipe you out.
And if you want to have to eliminate every civs city to win, you should have to eliminate the City-States as well
So I see
in game Options of
"Conquest Victory Y/N"... if N Conquered Capitals are autorelocated?
"Beheaded"..where losing your Capital either eliminates all your cities or turns them into Barbs or conquers them (eliminating you)