Can avocado act as an egg replacement for vegan bread
I think this is not possible.
Avocado is a great source of high quality fat, but does not contain any protein. Egg contains copious amount of protein which enables it as 'binding' agent. When protein coagulates it 'binds' the ingredients together, giving them a different texture.

So, avocado - having a completely different taste, texture and macro nutrient composition could not act as egg substitute anywhere.

On a side note - egg is not a vital ingredient in bread. Bread gets it's elastic consistency from wheat protein, while the CO2 bubbles from yeast make it spongy and airy. If anything, adding the avocado would be like adding potato and oil to your bread. It would have a harder time rising and the texture would be moister. Don't know about the taste, though...