Grab has recently added KrisFlyer to its list of GrabRewards partners. You can now convert GrabRewards points to KrisFlyer miles with the exchange rate depending on your tier.
Platinum members will be able to convert 11,000 GrabRewards points for 1,000 miles. Since it was just launched recently, there's an introductory double miles offer. Instead of 1,000 miles, you get 2,000 miles until October 31, 2017.
Gold, silver, and normal Grab users can exchange 12,000 GrabRewards points for 1,000 miles. The introductory offer is also applicable for these users.
I converted my points to miles and the transfer was fast. It's not instant, but it took them day. That's already good!