Well with todays technology the vf-1 and 0 without nuculear engines and transformation are very possible. The yf-19 even though it would be a strecth would be on the cutting edge of technology and would with a few more years of research also be very buildable with the thrust vectoring and forward swept wings (already on the experimental x-29 and su-47). The only real problems would be the missiles on the yf-19, unlike the vf-1 and 0 which have pylons, the yf-19 is mostly interior bays, I suppose it could hold 4 large missiles inside the bays on the legs but it couldnt hold the vast amount of missiles as seen in the anime (since I guess there arent micro missiles yet). Well, thats what I think about the matter, whenever you big airplane buffs get on to talk about this, im sure you will put my explanation to shame .