You make some very good points, at least in general terms. However I would suggest that the idea of a business plan needs to evolve rather than simply being tossed aside. The main reason being that a good business plan, at least in a traditional sense, creates a sound anchor (starting point) and description of the terrain/geography that needs to be navigated in order for a new business to be successful. The beginning point of a road map if you will.

This model worked well in the old slower paced business world but as you point out the dynamic now is such that change comes at a breathtaking speed. A more simplified business plan combined with a solid action plan that includes growth and anticipated contingency matters might be a better approach. Such a format would be easier to review and adapt with the advent of new technologies.

This second approach would be easier to work with in maintaining core vision as the project evolves. At the same time it maintains flexibility and adaptability.