All the merchants that accept bitcoin are not going to wake up and just start taking Litecoin or any other coin. They would probably just watch for a while before making any decision.
I dunno. It's now fully integrated with Coinbase which removes a lot of friction. Bitpay is a different matter but these people are in business and they're not going to tie themselves to pointless ideology and sentimentality when there's money waiting to be made.
It could happen considerably faster than we expect but only if there's demand. Right now I can't see much evidence of the desire to spend LTC.
When it comes to wages I assume plenty of them are going straight to dollars. In that scenario people won't really care what coin it is as long as there's a dollar portal.
Most merchants just don't really worry about something like this as long as it isn't impacting their sales though.
It surely must be right now for the more modest stuff. Why would you bother buying a Steam game when the fees eat up a quarter of the cost?