As of a couple months ago, Ethereum was averaging 50% of Bitcoin's transaction volume[1]. On June 11, Ethereum did more transactions than Bitcoin[2]. It managed this even though many of Ethereum's transactions are much more complex than Bitcoin's simple value transfers. According to the devs, the current version will top out around 10 to 12 tx/sec; Bitcoin has been stuck at 3.

So I think it's safe to say that Ethereum could easily absorb Bitcoin's transaction volume, even without Ethereum's planned scalability upgrades.

[1] http://www.trustnodes.com/2017/05/17/ethereum-reaches-50-bit...

[2] http://cryptoeconomy.info/2017/06/12/day-ethereum-processed-...