In reading Alan Kay's question on Significant new inventions I was coming up with answers that were not new ideas but old ones that have been passed by in the main stream. So, what significant lost steps forward that happened in a side track should be revived in the main stream of software?

These would be ideas that worked well in their context but a different context appeared and became dominant the context, even though it lacked the idea. It maybe that in the new dominant context one just cannot do something or it requires great effort to be exerted.