I think it depends on a) how the distribution of WC slots ends up, and b) how the change affects the qualification formats.

a) If the proposed allotment of 6 slots to CONMEBOL holds up, then I can see it pushing the confederation toward merger talks. It would have to result in a total allotment of 14+ for the united region for it to be worth it, though, otherwise the CONCACAF countries wouldn't go for it. If CONMEBOL gets upped to 7 slots for 10 countries, then it would probably defuse any plans to merge. CONMEBOL isn't going to the mat for Venezuela, Peru and Bolivia's sake.

b) Any arrangement would absolutely nuke the Hexagonal, and CONMEBOL's double round robin format would become a joke if it would take them 3 years just to eliminate 3 or 4 teams. You'll start seeing the top players not even bother to fly to South America for qualifiers. If the change in format means that Brazil, Argentina, USA, Mexico and the rest simply aren't getting enough strong competition in the lead up to World Cups, then expect there to be pressure to merge so they can create a UEFA-like qualification system.