1. If you're that worried and if you're buying from a shop / a firm, send the dealer an email or letter asking him the question. When he replies 'yes' tell him that you're buying the vest on the basis that it is compatible with new mags. If you find the mags don't fit, you are entitled to return for a full refund under the Sale of Goods Act (providing you return the vest otherwise unused.)
2. The magazine housing on the rifle is the same size, therefore the magazine is no broader or deeper than it was. It may be very marginally longer (I don't normally carry a micrometer) but it could even be a couple of centimetres longer and could still fit it most ops vests, so long as they have an extension strap on the pouches.
No problem on my vest. I think this is another old wives' tail.
There is a marginal difference between the A1 and A2 mags, the A2 being larger. The problem with the ammo pouches on the issue vest has always been there. The pouches were a tight fit when the A1 was in use. The marginal difference now just serves to make the situation worse. Later production for Telic issue was even worse. Early vests were made by CQC and are generally superior quality, later production is poorer all round. These later examples can be identified by the short strap hanging useless from the shoulders with half a quick release buckle on the end. All of the above refers to DPM vests, I can't comment on the very latest issue in desert cam but suspect the pouches may be a better size.
Many end users are removing the original pouches and replacing with the belt type, heavier lined webbing with Spanish clips and velcro (a better option for one handed use). If you go with this option make sure their professionally attached and remove all fittings from the rear to reduce bulk and weight.