Given the growth in transaction volume, it's pretty clear to me it will be the second, or possibly Ethereum will take the role of Bitcoin and fulfil the first:
Eth nodes are a quarter of what they were nine months ago. Most people can't even sync a node anymore. None of this is a surprise. This is exactly the outcome expected with unrestrained blockchain expansion. Bitcoin is about decentralization. Every other altcoin, it would seem, is about trying to invent an inefficient paypal.
There's more to decentralization than being able to run a full node on your Raspberry Pi with a 128K modem. Like more than 500,000 people in the entire world being able to write to the blockchain with any regularity, which is not possible with a 1 MB limit on the 10-minute blocks (1.67 KB/s throughput limit). With such limited write-access to the Bitcoin blockchain, the vast majority of the world will have to rely on trusted third parties to hold their Bitcoin wealth on their behalf, since it's impossible for the vast majority of the world to have write-access to the Bitcoin blockchain in order to make use of a private key.
I'd rather Ethereum users poll multiple trusted third parties to validate the transaction data they're seeing, and be able to hold their own private keys, and write transactions to the blockchain with those keys, than Ethereum users be able to validate the blockchain trustlessly, but have to trust third parties, acting effectively as banks, to hold their ether.
https://etherscan.io/chart/tx