OK my thoughts on these play test rules and the above debate on DD weapons.
(Warning, bit of a wall of text incoming
First, i like most of these weapons, i think some of the AP on some of them still needs some tweaking (Gauss longarms should have AP, the AP 5 for the full bore bolt action rifle seems a little to high i would of thought that AP3 or 4 would be a better fit).
I like the initial idea for destructive weapons, and the second idea as well (ignoring 50 points of armour per DD).
The reason why i like them?
Lets look at the rules as they stand, and the rules for building battle dress in the vehicle book. By using the rules in supplement 5-6, you can build a suit of TL15 battle dress, medium chassis, that will have a total armour of 24 max, plus extra armour (+6) and armoured coveralls (+2) for a total of 32.
This makes it just about immune to a lot of the 'longarm' weapons even with AP (though super AP from a gauss rifle will penetrate on a good roll) and that is fine with me, but it is not much protection from the man portable artillery that are the PGMP and FGMP family of weapons.
Based on pure average of the dice rolled for damage of these weapons, the TL14 PGMP does 12d6 auto 6. Lets assume that it is fired at said suit above on burst fire and the effect of the hit roll is +2. The damage on an average roll is then 42, +6 for auto rating, and +2 for effect, for a total of 50 damage. Battle dress stops 32 of this, so 18 goes straight though to the wearer. If that does not kill him, he is almost certainly now unconscious from the damage just caused to him.
Or lets auto fire on the battle dress wearer, and assume for the sake of this that all six dice pair up to create 3 hits on him, each with an effect of 2, so on average this means each shot does 44 damage, so 12 goes though each time, for a total of 36 damage. This will kill most in battle dress there and then.
This gets deadlier if the weapon used is a FGMP, which at the matching tech level does 16d6 auto 4(!) The average of that on burst fire would be 60, again just about instant death for the battle dress wearer. Even if we get a bit silly and build a ultra heavy suit which you could max out at 40 armour, the wearer of this suit is going to get seriously injure/ killed by the same tech level FGMP.
The destructive trait as first suggested, reflects this as well, battle dress is great protection against more 'mundane' weapons, but even it is not going to take a hit from FGMP or other man portable weapons (autocannon with super AP will go through a medium suit, let alone the anti armour gun that can be mounted on the suits or the mass driver cannon). Whether using the first idea, that armour is ignored and damage is x10, the result against battle dress come to pretty much the same thing, the wearer is going to take 30-40 damage on a 1dd weapons, and 70 for a 2dd weapon, which is a little higher than the above examples but the end result is the same, the battle dress user is now dead.
The same happens if it just ignores 50 or 100 points of armour as the second suggestion for DD weapons. So on the more personal scale i am happy that these weapons are destructive. DD weapons against vehicles is not something i have tested yet, and bear in mind that the current rules for making plasm/fusion weapons destructive/ultra destructive means that they can kill other vehicles with side/rear shots quickly (Sphere tank, 150 armour, fusion z would reduce the armour by 56 per shot, meaning second to third shot would damage/disable tank, and some of the current weapons with ultimate AP one shot it anyway ( heavy hyper velocity cannon ignores 90 armour).
I think that the new rules on DD still reflect the current reality of traveller weapons, and that the ignore x points of armour is possible the best for balance, but i would be happy with either in my games.
Sorry if this post is a bit of a 'ramble' and a bit rules lawyer, but i think the arguments above where not taking into account the current rules when it comes to plasma/fusion man portable weapons and by comparing them i hope to illustrate that little changes when you make PGMP/FGMP destructive weapons as suggested by these play test rules.