Haven't been diving in Mexico in a long time, but just read about this stuff and wow. Yeah, zero chance I'd ever willingly travel someplace doing shakedowns like this. Equipment for personal use shouldn't ever be taxed, and this has never happened anywhere else I've gone in the Caribbean or Asia/Pacific. As someone who travels with a camera/lenses/housing/ports/strobes probably totaling somewhere in excess of $15000 USD MSRP, it's just not worth the potential expense. And the ATA Carnet policies you can get aren't a whole lot better. Yes they let you avoid the airport shakedown, but they can cost almost as much (pre-paid).
From what I understand it's a poorly written law that customs agents are inconsistently abusing to shakedown taxes on anything that isn't explicitly an "underwater camera". So you might not get dinged for the camera or maybe the lenses, but they love to go after all the housings, ports, strobes, and other accessories because they can get away with it legally. But you may get lucky and get through for free, or they may tax you on everything including the camera or refuse to allow you to bring everything in. Who knows, because Mexico.