Will be interesting to see how big it gets, with the increased popularity of bitcoin.
The size of the blockchain has nothing to do with Bitcoin adoption. Blockchain's size increases with every block added to the blockchain, which usually happens every ten minutes. And each block being of 1 MB in size would increase the size of the blockchain by 1 MB.
Actually it has. You do not have to run a node to be able to transact. But you will be highly reliant on nodes that your wallet uses for broadcasting your transactions to the network. As a medium and large size business you would like to be able to control when you broadcast your txs, be sure that wallets do not falsify your balances, there are no MIM attacks. So having a node, thus, downloading blockchain is quite necessary.