It is supremely arrogant to think anyone else is interested in this stuff, but guess what, I AM supremely arrogant !
If you fancy running your own adventures in Jade, feel free. There is a whole world out there and much of it still unexplored. If you do detail any new areas, let me have your info and I'll try to merge it in with what I've already got.
I got the 4th Ed books when they first came out and I really like the new system. I've GM'd many, many sessions already and can see a lot of promise in it. Almost all the 4th Ed rules focus on combat and almost all the Powers are just different ways to dish out damage in various forms. In combat situations the games feel a bit like a computer rpg and I don't like computer rps much and never play mmorpgs either. At first glance this put me off, but now I'm over it. There will probably be a few more combats in my games than there were before but at least they should be more fun and more varied. Monsters having different powers makes them feel much more interesting. They aren't just 100 hit point 2d8 damage and AC20 any more. Zombies move and fight like zombies. Kobolds move and shift and fight and shift like shifty little reptiles that shift around a lot. This variety looks like it holds true for all the monsters.
Nothing in the new rules means you have to reduce the Role-playing and move away from story-focussed games. My games have always had combat in them and I do like there to be some dice rolling in each session. Sometimes we have no fight scene because there's a lot of talk and planning and sometimes we only roll a few dice but most sessions have at least a short fight and a few skill uses.
In order to make interesting combats in 3.0 and 3.5, I always added character levels and templates and magic items to monsters to give them a bit of variety. Like most DMs, I usually tried to do this "fairly" and levelled the creatures according to the same rules as PCs. Despite having some excellent software to help me (I used to use Role Playing Master by Luke Jones - sadly not updated for a long time), this still took a lot of effort, especially for the major npcs. Always a real pain in the a** when your hand-crafted npc gets taken down before getting to showcase their talents.
JADE has Druids, Barbarians, Monks and Bards in it, in fact all over it! This gave me a few headaches at first but the rules are now catching up (later books and dragon articles introduced the missing classes). Just Monk to go and I've provided a temporary Monk class.
I don't think it's feasible to convert high-level existing characters from the earlier editions. It's always a pity to have to retire characters that have developed over many years but "what the hell!". Time to start up a new campaign in the revised setting. The JADE campaign world has already been running for more than 20 years. The current set of characters have been adventuring for about 8 years or so. The previous set lived (and died) through about 60 sessions worth. Sad to let them all go, but hopefully the new characters will get the same sort of emotional buy-in after a few sessions.