Feature request: command to change motion speed

Something that is really hard to do in minecraft is manipulating the motion of an entity or player, to get a projectile to go faster uses thousands of commands, and to change the motion of a player is almost impossible, you need to teleport him in the right direction and to change the speed is very hard when also making it look smooth

So what i would like to see is a
"/motion" command, so it would be:

/motion [entity/player] [x/y/z/all] [+,-,/,*,%] [amount]

You have proven to be able to change the players motion and speed of that motion by giving us the levitation effect, but if it is too hard to make it work for platers, that's fine

You have also shown us you can multiply, add to and retract from numbers with the
/scoreboard players operation

This command would save many people a lot of work and lag and make us able to make guns, low gravity, graphs and so much more!!!

Please Mojang,
For us? ;')