That means that they are not going to receive security updates, among other things. Well, not exactly true -- mips24_kc packages will still continue working, though newer kernel modules will no longer be compiled, meaning you don't get the benefit of the updates and improvements that e.g. kmod-ath9k is still getting to this day.
If you need cheap routers, I have a stockpile of Meraki MR16's (2.4GHz + 5GHz, 2x2) -- which share cases with the MR12 (2.4 only), MR62 (2.4 outdoor) and MR66 (2.4+5GHz outdoor) -- which accept PoE, were already ported to the ath79 target, and are deployed extensively at Newport Wireless Mesh. I'm happy shipping them out, flashed, for the cost of my labor to anyone who is interested in also owning a small portion of a stockpile. (I paid something like $3 a pop after shipping and taxes, so I can definitely beat whatever price you can find for stock-OpenWrt-friendly devices.)