Pretty sure there will be no needs to add any more coins. Right now the BTC mempool is almost empty, you can literally get your transaction confirmed with only 5 Sats/byte or so.
That and also Segwit might get activated within 2 months which should provide a little bit of scaling.
Actually each new coin added gives Bitsler some extra edge against competition.
Some prefer certain coin for speed or privacy; many just love to play with whatever coins they mined.
I don't know how difficult is to add new coins, since if they get too many, Baryom can very well start a crypto-exchange side business too

but I think that more coins the merrier.