I don't see how it's that big of a deal. If you're glancing or penetrating a vehicle, you're getting a result anyways, even if it's just a shake. Like you said, wargear can improve the odds of survival, but it's only the odds (never a sure thing), and wargear like extra armor is only available of certain vehicles anyways.

All a system like hull points does is make the vehicle damage system more deterministic over time, meaning it flattens out the probability curve of vehicles absorbing an unusual number of damaging hits through luck. You'll no longer see the super Rhino that take penetrating 10 ML hits and keeps on trucking because they were all shakes.

For the system to have any real effect on overall gameplay, the number of hull points would have to be lower than the chances of destroying the vehicle through the damage chart. For example, say a Predator has 6 hull points, and a penetrating hit does 2 hull points of damage. Three such hits will destroy the vehicle...but three such hits will also give 3 1/3 chances to destroy the vehicle through damage. All that's really happening is the elimination of statistical anomalies. Over time in thousands of games, the net result is to make vehicle damage more predictable, and less susceptible to random runs of luck.

Of course, that's just an example based on one possible system, but that's likely going to be the effect of hull points. I suspect they will closely match the odds of being destroyed through the damage chart. If it works out that they get more hull points, all that will happen is very unusual runs of luck will be eliminated. If they get less, then vehicles would take a true hit in terms of survivability.