If you want to be able to use it for day to day purchases you need really fast confirmation times otherwise you will have to go through a centralised service like BitPay.
I would say the new DPOS blockchains will offer the fastest reliable confirmations. (The first one BitShares X will offer BitAsset trading, BitUSD, BitGold etc. & you need fast confirmation times to be able to trade.)
http://wiki.bitshares.org/index.php/Why_choose_Bitshares%3F
True. Merchants would definitely have a big advantage with it.
I know people who refuse to accept bitcoin due to long time.