Well I think overall, I'm sure there will be an increase in merchandise. But it's just variable in my opinion.
I was under the understanding that "National Team" and "U21 Team" had very different meanings when it comes to merchandise; i.e., the former actually paying a merch bonus while the latter does not.
I think it all comes down to softening the salary paid by team that own NTers, which is not that big of an issue with U21 players.