I like the idea and would've been something nice that BB could have had if that's how it started. However I see one huge issue with this with the current system:
Training Camp means more pops added to players than without it. Because of this, it would mean that eventually the players in BB will be better than before and their salaries will be higher as well. With the best players already becoming too expensive (centers especially) for the best teams to afford and for everyone else, become bankrupt, this would only escalate that problem. Players being better than before means the players ratings, records, accomplishments would be greater with the change and the players skill set will vary more. It would be almost like baseball when the steroid era begun.
The other big problem, is that if it's implemented, it would mean that with users knowing that young guys can improve and older not as much, it would inflate the value of young players and deflate that of old players. I'd personally want to seek young players if thats happening because I like to take advantage of the more pops that can come. There is also need to consider that young players right before the season ends would be more desirable than the beginning because it is right before training camp where more pops can come and then their value is worth more. But then again users would be smart enough to know it so bidding would be higher before season ends anyways but it's something worthwhile to point still.