You can already enter a drop-off location. It might be that Uber needs to make this feature more pronounced in the UI. On the confirmation screen, you can tap

You can already enter a drop-off location. It might be that Uber needs to make this feature more pronounced in the UI. On the confirmation screen, you can tap a little plus button next to the pickup address to enter your drop-off location. It's come in handy for me a few times.