i like option A. and since it counts towards Gameshape, it is punishing enough as such. i doubt teams would want 100k players to sit out a week just for some training purpose... However, if you want to be safe, you could put a salary limit in combination with option A. that would take away any incentive use it to train side players. Alternative to the salary restriction would be an age restriction, but the age restriction should be low enough (i'd put it at 22 or 23, which is the age you can train allstars or perenial allstars before they start being hard capped).
i reckon that if the salary is high enough, you won't want to give them 48 minutes, meaning they can't play for the team during that week (unless you sacrifice their GS). so for that reason, i'd be more in favor of adding a age restriction ontop of your option A, instead of going with a salary restriction (cause then everyone will be making SF's...)
I can see the merites off it. you'd get more talent out on the market, which could bring some prices down, while giving faster improvements to teams who do train players, meaning they can go up faster.
I'm not seeing any downsides that hugely outweight the upside the idea has. Although it might be hard to implement. still, i like the idea if there is some trade off to the free training minutes. the examples clarifies enough for me. up to the BB's to check it out now.