If he is talking about computer science, then there probably will be more powerful abstractions discovered. If he is talking about software engineering, I think it will be a challenge. Just as there is not theoretically perfect design for a vehicle with cupholders and stereos, I don't think there will be a perfect abstraction for designing the next twitter. The underlying fundamentals may see drastic improvement, but I think we'd just take those and glom on even more cruft with our newfound abstractions.