No, but they should support forks with significant hashing power and exchange value behind them.

BCH has ~2% mining power behind it. That's not "significant".

According to what definition? 2% of BTC mining power is still more than most other coins.

Coinbase doesn't support most other coins either. There are exchanges that are enthusiastic about supporting all of the altcoins out there, but Coinbase isn't one.

It's already in the top 4 coins in market cap. Seems like a reasonable coin to support at this point.

That market cap is illusionary because there's no way to deposit BCH into exchanges right now. ViaBTC apparently requires 20 confirmations which would take about a week at the current hash rate, the other exchanges like Kraken and Bittrex aren't accepting deposits at all and don't plan to for a few days yet. So essentially all of the BCH making up that market cap cannot in fact be sold at all right now; the only BCH can be is from Bitcoins that was in exchanges that support BCH at the time of the split.

Market cap is not a useful metric. It hase very low liquidity at the moment.

It's been extremely volatile so at this juncture price means little. Give it some time before arguing it has any value, the market hasn't decided yet.

Right at this moment it's values at $717.00 per BCH vs $2694.42 for a BTC.

You'd argue it's better for me to have wait until the price stabilizes at 2% of BTC before I'm allowed to cash out?

Depending on the interest in the coin I would say yes. Not doing so will cost them customers.