When CoH2 was in alpha/early beta, all commander-specific units had to be built from tech structures. The main problem back then was these commander-specific units replaced existing units instead of simply adding to the number of units you could create. For instance, Guards and Shocks replaced Penals, the upgunned T34 replaced the stock T34, etc. That was an imperfect solution because it ended up limiting your options; if you didn't have enough fuel for the upgunned T34, you were essentially screwed, since you couldn't produce the cheaper, weaker variant at all.
Maybe this is a soultion.
Call-ins requiring tech-up.
But not replacing existing units.
Just requiring tech-up.