Hideeho
On a more serious note...
What would you change from the b4.2 to make a b5?

+7 more on chassis? Been there, done that, all but ready to come back. It's easier to drive when the skill level is not that high, but as my skill level is increasing & I'm about to the point where the shorter chassis & quicker handling would be a bigger help than slower reactions when sliding.

Aluminum chassis? Seems like a good idea on the surface, but the plastic chassis flexing helps the handling. If an aluminum chassis flexes any significant amount it will bend or warp. Just ask the 22 drivers.

Carbon fiber chassis? Again seems like a good idea, but again no flex or it breaks. Then again cf works very well for the b44 series & Schumacher. I would think cf would be a better option than aluminum.

Narrow nose with longer, maybe gullwing front arms? That's a possibility, but if its too much narrower there will be structural issues.

Redesigned front end to allow adjustable kick up, like an 8th buggy? This would be on top of my list if I were working on it.

Easier/more adjustable rear anti-squat/toe? This would be #2 on my list. Again, look at how a 1/8 buggy does it.

Mid engine? Jury is still out on this one, but x-factory seems to be able to get their cars to handle on dirt pretty well. I would be HIGHLY interested to see what AE could do with the design concept. Making it convertible is terribly convenient, but is terribly compromised, unless the conversion is a huge conversion & requires a ton of parts to do.

A true limited slip differential? This would have as big or bigger impact on the rc world as lipos & brushless combined! But, I don't think it's doable for a reasonable price.

What else would everyone like to see on a b5? Keep in mind a b5 would probably start with a clean sheet of paper, so the sky is the limit.