Is there a speed graph (like the speed graph in After Effect's graph editor) in Houdini? The default graph view is a value graph, it shows how the value of a channel change over time. I personally find the speed graph really intuitive and easy to create the animation I want. If there is a speed graph in Houdini, how to enable it? If no, does SideFX consider implementing it in the future?

That's a very good request! You can use the areaCHOP to view the first derivative of a channel, aka speed. Direct editing isn't available unfortunately afaik.

Please use the Support menu above to file an RFE - request feature enhancement.