I agree, even though its not a particularly big issue for me. yet, if you want to show different construction phases, would you not need at least 2 - 3 in-construction phase models of the same ship type? sure, you can modify them based on the final model, you could even use the same basic template for the very first phase for all ships in a class. still, it sounds like a lot of work for something which is, at least for me, not a primary concern.
for examples, I think conquest: final frontier did a very nice job of phase-wise exterior construction of ships and stations.