My hypothesis is that in a few months, we are going to begin seeing people die by thousands.

This will happen as the cells that received and expressed the initial mRNA payload will either reach the end of their natural life or they'll go through apoptosis one way or another. Once that happens, the immune system will react to the contents of the cell that is now in the extracellular matrix and respond with a cytokine-storm like event that will be attributed to a mutated (likely the Brazilian) variant.

The reason why we are seeing the elderly exhibit this earlier is because their cells are going through apoptosis more often.