This change has no effect on HQ-produced units at all. Their advantage has always been their ability to be produced without having to spend time building a structure, and their ability to be produced in tandem with units in other structures. The fact that they might lose a few seconds of travel time because they can't spawn as close to the field as other units will have a negligible impact on balance.
Stop thinking in terms of balance impact. This community's obsession with balance is infuriating. Balance impact is impossible to predict. This is a design change, not a balance change, and it's a clear and obvious improvement over the current design. Worry about balance when there's actual reason to worry.
It may be a design improvement in 1v1 and maybe even 2v2, but in 3v3 and 4v4 all it will do is make the units of those who got unlucky take much longer to reach the fuel. For example, if you're playing bottom as OKW on steppes, and you need an Ost MG42 to come to your side so that you can lock down the bottom fuel point, normally the Ost player would just set his rally point on the bottom so that the MG42 spawns on the bottom. If the design change was implemented though, his MG42 would come 30-90 seconds later than it would normally, which is more than enough time to lose island on steppes. Sure, if he spawned on the bottom, his MG42 might come a few seconds faster, but if you get unlucky and your Ost player is on top, there's a decent chance the MG won't arrive soon enough, leading to you losing that side and, due to how steppes works too much of the time, the game.
What they really should just implement is a per-building option to choose whether the unit will spawn at the rally point or at the tech building itself. That way, all players can tailor their base to the style they choose.