You thought DDR4 was short lived, how about DDR5?
As always with PC hardware there will be constant innovation that will make your previous large investment void. Fortunately with DRAM, this doesn’t normally happen for many years, most people can live on 8GB, which we have in single sticks of DDR3, a very large benefit of this is in smaller systems, where there are fewer ram slots, with DDR4 you can run 256GB of RAM in 2 slots. (If supported of course)
Naturally, we don’t have any evidence, but if previous generations are to go by we are going to see the densest capacity RAM for many years. First of all DDR1, we had 1GB sticks, DDR2 became 4GB sticks, DDR3 eventually became 64GB per stick with finally DDR4 becoming our current largest at 256GB (using NAND Flash, so there is more of it but its response time is in microseconds compared to Nano seconds) If this trend continues we will be seeing 1024GB / 1TB single DIMMs in servers. This is insane, if a E7 Xeon supports 16 Sticks, along with 8 sockets per system, we could be looking at 131TB of RAM INSANE.
What does it mean for the average consumer
If the value of DRAM changes on a trend as it has done every generation, we will be seeing 16GB as a starting capacity in the majority of PCs with 32GB in a few more PCs.