The question : Civ 5 dead or not ?
It seems too blunt a question, and I say no because civ 5 already has the potential to keep going. Unless civ 6 covers every single major issue with civ 5, I see no point with civ 6. Or if civ 4 fans expect some of their features in civ 6 then I imagine a combination of SMAC and civ 5 in civ 6:
- stacked units, but maximum limit set to something like 3 (max 1 melee, max 1 ranged, max 1 non-combatant including general). Same applies to ships.
- any successful melee kills against one stacked unit will damage the rest of the group a fair bit.
- artillery is weaker against units but does collateral damage on stacked units.
- non-artillery missile units are (again) weaker against cities and have only +1 range but they can also cause some collateral damage but not as much. If rocket launchers are in game, they deal more collateral damage.
- City stength grows much more slowly until renaissance era when it grows faster. City bombardment still exists but its range depends on whether it's on a hill or not. Cities also have some resistance to collateral damage (about 50% reduction depending on defensive buildings).
- melee siege gear is available to all civs not just Huns and Assyrians and they have bonus resistance to missiles but a combat penalty against melee attacks. Continues until end of medieval era. Missile artillery has double combat bonus when attacking them (stone vs wood + steel ram/tower? Should take out a lot of HP)
Conclusion: if many people agree with these combat rules for civ 6, then I change my mind and say yes, civ 5 may well be dead.