it would be cool if you could browse the shop in 3d and pick up and examine 3d products
That would annoy the flip out of me; unless it was very well done.
Could 3D improve product presentation in an online-store?
Providing it's well done, not over-the-top, and it's quick loading.. If it's an essential part of the store (i.e. you couldn't use the store without it); then only if it's compatible everywhere, or a compatible alternative provided without having to look for it: one thing I hate is: 'You can't view this page because you don't have latest version of [insert as applicable]'.
Real estate trade is not the only shopping field where you can apply 3D solution effectively! You can also use 3D for selling such merchant as watches, apparel, electronics, furniture etc. There is no doubt that 3D view provides customers with more detailed information about the product retailers sell online.