Aside from this being a balancing nightmare and that it would kill the vast majority of kills and traits there are other practical problems.Let's say I'm a Guardian and pick Elementalist as my dual class and slot Air Specialization. How is the Minor Adept trait, Zephyr's Speed going to work? The trait: "Move faster while attuned to air". is my Guardian going to get access to Air Attunement and permanently be attuned to Air? How is One with Air, that reads: "Gain superspeed when attuning to air." how are you going to attune to another Element before going back to Air to get this bonus? What's Fresh Air, that reads: "Recharge air attunement on a critical hit. Gain a ferocity boost when attuning to air." going to do? Are you going to get access to all Glyphs and use only the Air version? What if I'm a Druid, will Inscription, that reads: "Grants a boon associated with your current attunement when you cast a glyph. Reduces glyph recharge." work on my Druid glyphs too? There so many complications when adding a specialization from one profession to another. You can't use druid with elementalist air traitline because it should be put on your last traitline only, you can't be druid+ele but only ranger+ele; yes that will be hard to balace, but your suggestion is good, you spec air traitline, get glyphs as utility, but they can change how they work like "using a virtue you get a boost in ferocity" for fresh air trait. It's hard to do that's for sure, but not impossible, there are many solutions!