Only thing I could recommend is to share more of these team's considerations/plans so people on the forums can better channel their feedback and senseless discussions like the above can be avoided. If you guys can find the time, of course.
So this is all probably more than I should say.
I think there's a very clear reason why we (and basically every game company/dev) aren't more open.
Just check back to initial the 221/223 suggestion on the commander feedback thread. A lot of people were coming at the idea and assumed a lot of things that weren't necessarily true. The idea was to ask if the idea of the unit was interesting and had potential. Even though nothing solid about the unit was given (because, honestly, nothing solid about the unit was decided), people made their own assumptions about what the unit was going to be and why the unit was a bad idea because of it. They started to oppose to the concept of the unit without knowing how it would even work and how it would actually be like. Because of this, I imagine impressions of the 223 when it actually was implemented were more negative than they needed to be. While it honestly did makes us more aware of a few things to consider with the implementation of the vehicle when it came down to it (pop cap, cost, etc.), most of those issues would have been ironed out with feedback after the unit's release anyway.
Similar to that, others were starting to doomsay in response to a 221/223/concept we weren't even quite sure we wanted to go with. Essentially, they started to trash on the team for even considering an idea... Personally, I prefer to be trashed on and lose reputation after I massively screw up, not before
In a slightly different vein, you probably realize that Andy is the main person delivering all of the official information. He works for a company, officially represents this company to the community, and has to maintain a professional reputation in this community. Sharing ideas on the forum before they're potentially ready kind of skirts this line of being an official presence. I think it would honestly be unreasonable to expect him to share this much when he directly represents Relic's brand and is expected to remain professional.
As for the non-Relic members, the identities of the people on the balance team were not disclosed and there's a reason for that. You saw how...personal people got about the last revamp and balance patches. Honestly, look at how heated some people got about THIS revamp. If Andy delivers the official changes, then feedback usually remains constructive and useful. If an individual on the team (besides Andy) shares anything about changes, then they personally become a target, and people who dislike the changes start to attack them. Feedback then seems to become less about the changes, and more about bashing whoever is deemed responsible for them (in this case, that would usually be the person who shares the change). Asking a member of the team to go on the forums and say "hey, we're considering this direction, what do you think" is potentially asking them to be bashed for an idea that might not make it to the actual revamp preview and which might not even be theirs - again, all without facilitating meaningful discussion about the concept in question.
That said, the spawn in with kars is: a low risk change, something we were convinced was a good idea, almost certainly going to make it in to the next iteration, and going to stop a bunch of users from flaming and arguing with each other.
Honestly, the last reason was why I let everyone know, otherwise, the ~2-3 day wait for the next iteration's notes to be officially released is usually fine.