mach1.9pants said:
Yeah multi-classing is my 'if we had the Rouse on the water board' question. So, a table detailing the effects of m-c. Mmmm, that certainly restricts what they can do with future classes because they will all have to comply with a template to allow m-c (and I suppose other things). Still it sounds really interesting, I hope it works

This is (probably) telling us that classes will advance and gain powers/features etc in a very uniform way. Hopefully that makes custom classes easy to make. Also hopefully we won't see an avalanche of classes in splats etc that have little to differentiate them. It will take a fair bit of work to make a full, different interesting class (i.e. a dozen or so features and 80 or so powers, I suppose) you can't just use the wizard's/cleric's/etc spell list like in 3E! I really hope that the classes don't end up as bad and as boring as the bloodlines from UA *BARF*
Matthew L. Martin said:
I think that if you "really want to go into a completely different direction", you'll be using the rebuilding options they've hinted at. Thus, if you start as a fighter with some wizard elements but decide you'd rather be more of a wizard, you could rebuild as a wizard with some fighter elements.
This is speculation, mind; IANADOP (I Am Not A Designer or Playtester).
About class creation, yeah, it will have to take an extra effort to implement the multiclass abilities.
For example, if I want to post my own custom class and let other be able to "dip" into it, I'll have to create a table that specifies what you get with the first dip, what you get if you want to go further. It may seem difficult, but once we'll see the rules, it might be as simple as every other development for 4e we've seen to date (monster and races for example are really easy to develop!).
The way the classes will advance is surely mostly uniform. Only the few key class features (like rogue's sneak attack) are a little more arbitrary.
But yes, from what I see, developing custom classes will be easier. Or better, it will be easier to make them follow the quality standards, not necessarily be simpler, since you now HAVE to develop a whole power list of at least 60 powers.
Good thing is that you can start by making the heroic tier progression and then add the other tiers once you're sure that the first is balanced. Good idea for my first custom 4e class.
About classes in splatbooks, I'm pretty sure that books such as Martial Power won't have new classes, only new Paragon Paths and new powers for existing classes. And that's a wise choice: new classes relegated to new PhBs that come annually and with a higher probability of having REAL QUALITY content (classes).
About classes ending up as boring as bloodlines, it has been a little of a concern to me too. Initially, the most demanding players I think we'll see them like that, after some months of initial excitement. But "splatbooks" adding new powers and options are just made to "feed" those type of players (like me).
About retraining, being multiclassing like this, it will be really necessary. Because if at some point you see that more than being a Wizard with Fighter training you want to be a Fighter with Wizard training, you should have means of trading your Wizard levels for Fighter levels and your Fighter training feats for Wizard training feats. I hope they'll make rules for this kind of situation that I would call "surpassing the multiclass threshold"...
In the end, I'm so teased that I'm really counting the days towards June the 6th.