i dont think DDR4 will be all that special right away, the specs for max DDR3 have overlap with DDR4, and then theres the cost of the new ram, and the fact its a safe bet AM4 cpus will be compatible with AM3+

AM2+ lasted up until.... more than now... since you can drop a thuban into AM2+. i would say that platform dies once BD is out. if anything its AM3 that didnt last very long