Unfortunately, one of the fundamental aspects of FFXI's Skillchain system and thus, the concept you've developed (that is, elemental damage) is utterly useless here given the fact the elemental wheel is neutered. So a weaponskill's element would be nothing but for dramatic effect. Besides, SE did have a sort-of skillchain system in FFXIV 1.0, called 'Battle Regimen'... which didn't work as well as it should have, so it was scrapped when Yoshi took over and redesigned 1.0's battle system to something more similar to what we have now.

Another problem that was particularly notorious in FFXI with this system was the fact it fostered 'job favouritism' for the aforementioned element-bonus. Certain Jobs were used to exploit the magic burst effect and certain Jobs that could make use of certain weaponskills, and other Jobs were ignored. FFXIV's system is designed specifically to stop Job favouritism, so the magic burst system simply would not work here.

Also your idea is not too different to the current weaponskill combo system we have, only made far more complicated (perhaps unnecessarily so) - why make things more complicated simply for the sake of complication? Given the game is designed specifically for new players and those of more moderate skill, over-complicating things just goes against this idea I'm afraid. Your concept was well thought out, but sadly, for these reasons, I don't see such a system ever being implemented I'm sorry.