Whaaaaaat ??? Model 3 does not have the 3G issue that 2012-2015Q1 has. In April 2015, the first Model S's had LTE, so before that it was 3G.
There will need to be a plan to move the remaining S's to LTE before the shutdown of 3G. Funny thing is that, some of these will not be Tesla's problem by the time we work through most of the remaining time. Between MCU1 replacements, MCU2 Upgrades, Tegra board swaps that owners will opt to pay for LTE upgrades too, many of the fleet that have not already been replaced will be in that column that still need it.
And Tesla provides those cars unlimited connectivity. So, at some point, before those remaining cars lose 3G connectivity, Tesla will need to upgrade those cars so the cars still can be connected to the mothership. I bet Tesla will drop the price to half or less - and might even be compelled to pay for all of it because by then, they will want/need those cars connected to the mothership as much as the owner wants their cars connected. Sure, WiFi, will still work.