I would like to second the notion of posting errata documents for every product that you produce, and making them a sort of living document, where your customers know that if they have version 1.2 of the errata, and there's a 1.4 out there, there are more changes or recommendations to be had. People slammed WotC for this practice when their D&D 4th Edition came out, and they immediately started tinkering with the rules, but I appreciate that level of immediacy and the feel of applying "patches" to the game, much like we do with software when bugs are found. And eventually, it became a standard, and now people want it everywhere.
What to include?
New examples - that's an easy one, now that the rules are set.
Fixes for problems - pop-up turrets, for example, are contradictory, and will need to be clarified
Missing info - still not sure if it's just me, or if there really isn't any set rules that made it into the book to determine how much cargo capacity the vehicle has when all is said and done (specifically the translation between spaces and kg/tons). And a simple table with each vehicle included in the book, the chassis it was built on, and the number of spaces it was assigned (though this is a two-edged sword. Those of us that will want to will reverse engineer the vehicle and make the mods we want to make, but some of them will surely find other problems where the math doesn't jibe with the rules!). And I'd like to see rules on retrofitting specifically laid out, like you do with adding armor after the fact. I want specifics on how you should go about adding machine guns to a standard ground car or the like - it's the sort of thing that shows up in games (and in montage sequences in movies) after all.
That said, I don't want my comments to come off as being angry, or indicating that my review will be a negative one. Just an area where improvement can be made in an existing product, honestly. The rest of the rules look solid. The battledress design rules are particularly intriguing and make me want to run a military/mercenary campaign just so I can use them. I was concerned that, in streamlining things, the flexibility would be lost, but the chapter on overall modifications, applicable to any type of vehicle, was quite good, with a great deal of breadth that alleviated that concern immediately.
As someone who is unashamedly a Mongoose fanboy, a fan of their books and of the IP they've chosen to associate themselves with, I just wish there was a way that I could afford to volunteer my services as a playtester/editor/reader so that, in addition to last-minute "we changed some rules, and so the examples are now broken" issues being caught, I could help with every "loose =/= lose" and missing parenthesis problem as well.