Well, that's assuming that what we saw in the preview is indeed the final version of 8+2 (assuming it'll exist in the first place), it's possible that in FINAL proper it'll have a very difference appearance, less clean and more crude to show how the "fusion" was made in urgency, and also an explanation of why that thing was even necessary in the first place since EVA-08 only got superficial damages.
Maybe there'll be another battle near the beginning of the movie where Unit 08 get trashed and require to have part of EVA-02 cannibalized to repair it in time?
BlueBasilisk wrote:Edit: Eva 02's head and mechanical arm definitely look like stopgap repairs made on the cheap, but Wille had the resources to upgrade and re-armor both of their Evangelions, which makes me think the head and arm are deliberate upgrades instead of a quick fix.
I had a personal theory about that: at first, 14 years ago, EVA-02 was indeed repaired hastily to have it ready to fight the remaining Angels, or maybe it happened just after NERV split and the just created WILLE didn't had the resources to properly repair it and resolved to use cybernetic parts. But later as WILLE stabilized and got more and more resources, they ended being able to have a gigantic fleet, a giant flying flagship and various new weapons and armors for the Evas, so repairing Unit 02 became possible, but that cyborg head apparently works as fine as the previous head, and those robot arms gives the Eva a lot of tactical versatility, so why bother? Better just upgrades the cyborg part to make them catch up with the new armors!
Besides maybe Asuka requested to have her unit stay like that: she has gone through extremely tough hardships and came out alive, stronger but scarred, so for her her Eva, which came through similarly big hardships, should also keep its battle scars. For me that feels very IC for Asuka.