I never considered alien infiltration much of a problem. The original game was hardcoded so that the aliens never infiltrated Russia, meaning you would never lose because all the coutries quit. By the time you had reasonable radar/decoder coverage, so you could have a reason to gripe about infiltration being hard to stop, your main sources of income were selling loot and manufacturing lascannons, so losing a country or two meant next to nothing.
If the OXC follows the no-infiltration-in-russia rule (and I hope it does) the impact infiltration has on gameplay is next to none.
It's not really about gameplay, or "boohoo aliens cheat I can't win!" since indeed the funding you get is rather small after even just a few months of recovering stuff from UFOs.
The issue is the immersion, the self-consistency of the setting, where it makes no sense that some missions cannot fail. If the country is happy and you shoot down the alien diplomats, then the country should not defect. Having automatic success makes the game feel scripted, instead of fluid. And I like XCom because the game is fluid in general. There's no script that's followed and predictable, (almost) everything happens just by following sensible flow of events and consequences of success/failures.
As a workaround, I am thinking of looking into saves and reinstating countries that defected "wrongly", but with a significant decrease in funding, to represent that after the alien mission, they are much less enthusiastic about the XCom project.
