as a student trying to design a theoretical circuit I'm just trying to see if it's possible, and maybe some of the reasons why, or why not
OK, let us try and channel your thinking.
1 How much power does the motor require?
Without knowing this, all other considerations are moot.
2 What range do you anticipate between the RF transmitter and the RF receiver?
As mentioned else where, if you are relying on true electro-magnetic coupling, the inverse square law applies.
ie as you double the distance between tx and rx, so the received energy drops by a factor of four ( ie 2 squared).
If you are relying on magnetic coupling, you start to encounter an inverse cube law.
3 What frequency do you plan to use?
A higher frequency would allow the use of directional antennas, radiating the RF energy in the required direction. This would improve the range, but the inverse square law still applies.
Also don't forget that you cannot just park a great big transmitter on any frequency you like. You are likely to make the existing users of that frequency very angry.
4 While on the subject of frequency.
It is fairly easy to rectify RF power up to a few 10s of kilohertz, just use the same sort of diodes as used in switchmode power supplies.
But when you get into the MHz region, rectifying significant amounts of power becomes more difficult.
You my be able to use an active rectifier scheme...
Who knows. It all depends on the amount of power you need to rectify.
So, does that help with your theoretical study?
JimB