Yeah, this is a problem with high density DRAM. Fixes are possible but difficult and expensive. In the cutthroat DRAM market nobody seems willing to put in the engineering effort to develop a solution and then manufacture it. It would have to sell at a premium, in a market where it's difficult to even find ECC memory at times.

The article states that ECC isn't sufficient to solve Rowhammer, but it does make the attack harder. If you are looking for a hardware solution it is your only option currently, even if it is imperfect.