Can 5okW be transferred using resonant wireless power transfer?
Your question contains several inconsistancies and things that don't make sense.  You apparently want to transfer a sizeable amount of energy wirelessly into a car from some sort of transmitter.  You say you want 50 kW energy transfer rate for 2 seconds, which is 100 kJ.  Now for the inconsistancies and problems:

You say you don't mind "efficiency loss" (inefficiency?) in the question, and that you are "not concerned with energy loss" in a comment.  Let me be really clear.  At 50 kW efficiency is a big deal.  Even if you don't care about wasting energy and its economic and environmental costs, dealing with the heat will be difficult and expensive.  Let's say you have 50% efficiency.  That means to get 50 kW to the load, you have to supply 100 kW and that 50 kW of that will make something somewhere get hot in a hurry.  This is not something you get to ignore.

You mention storing this 100 kJ in supercapacitors.  Do the math.  Today you can get a supercap that is rated for 5 V and 1 F that is around 1 cubic inch in volume, or about 16 ml.  The total energy it can store (ignoring that you'll never get all of it back out) is 12.5 J, which comes out to a volumetric energy density of 780 J/l.  To store your 100 kJ would require 130 l, or a cube about 1/2 meter on a side.  Note that this doesn't account for mountings, invevitable spaces between individual caps, interconnects, room for airflow or some other means of cooling, etc.

You basically want to create a transformer between a primary burried below the road surface and a secondary in car above the road surface.  There will be some inevitable minimum separation between these, and the magnetic leakage field will be large.  Anything in the vicinity that can conduct electricity, like the metal care frame and other mechanical structures, are going to have eddy currents created in them.  A large metal object like a car frame can dissipate this power for a while, but it will rob power from the magnetic field and lower the Q of any resonance you hope to set up.

Put another way, the intended pickup coil will only be a small part of what the magnetic field produced by the transmitter "sees", so it's characteristics won't have a large effect on overall operation and won't intercept a large fraction of the total power.

The inevitable large transmitter field is going to effect everything in its vicinity, including any people in the car.  I'm not going to sit my butt in a 100 kW (at least) magnetic field.  Even if you can shield occupants and only .1% of the power gets to them, that's still 100 W.  Have you done careful studies what a 100 W magnetic field at 10s to 1000s of MHz does to a human body?  Even microamp currents in the wrong place in the brain or other parts of the nervous system could possibly cause trouble.  And what about long term effects?  Can you show that repeated exposure over 10s of years is safe even if a single exposure appears to cause no immediate harm?  I didn't think so.  There is still legitimate scientific debate over whether a cell phone routinely held to your ear has any long term effect, and that's a rather lower power level and is largely a electric field.