I'm not a huge fan of them, but 4240 screen is the smaller/simpler Gen4 screen. But if you "just need auto steer" it would be likely the cheapest way to get that in a newer generation of screen and no annual fees. The 4640 is the larger screen that's the direct replacement of the 2630. If you only need autotrac, again it has that in base permanently. It'll cost more since it's far more capable of a screen and it's larger. 

The G5 Plus you could get with permanent autotrac and section control if you wanted. Costs the most but it's the nicest, biggest screen made and the current new model. 

So....could you go to all 2630's? Yes. But both the 2600 and 2630 have little to no support from JD. Which for some (many) people that's fine. Brown boxes still work and they've been "unsupported" forever as you've seen already. 

2630 - slightly newer screen (Gen 3) and tons of them out there yet. You can get screen replacements if one goes bad. Same layouts and button locations as you're used to. No annual fees

4240 - smaller, more basic Gen 4 screen. Cheap way to get into Gen 4 for auto steer only situtations. No annual fee, new screen layouts and buttons

4640 - full size, full featured replacement for the 2630. No annual fees for Autosteer only. There is a fee for section control. New button layout

G5 Plus - Super sized wide screen with permanent autotrac and section control. No fees. New button layout

The "new button layout" on the Gen 4 and G5 takes a little getting used to but it's FAR better than the 2600 and 2630 once you've used it.