I don't think it is purely coincidental that Gateway stopped responding to emails at about the the same time that gamerequest1 posted the video proof of the Gateway brick when using Diagnostics which I believe was on February 20.
They probably genuinely believed that Gateway users were not at risk of bricking their consoles. But when a repeatable method to trigger bricks was found, they probably suddenly found a ton of work just dropped on their laps before they could release Gateway 2.0 without exposing users to the bricking risks.
They would likely need to isolate the exact function or functions in diagnostics that trigger the brick, then do a lot of tweaking and testing to try to ensure that the bricking problem is resolved. This would be particularly problematic if the offending functions are called only occasionally during normal use but heavily during diagnostics which is likely because we have gotten complaints about bricks being triggered without going through diagnostics but can only repeat it through diagnostics.
This kind of troubleshooting is probably going to be a major undertaking, particularly since you need to restore your 3ds each time it is triggered which is not only time consuming but also blocks off a lot of methods you could normally use to debug.
So it does not seem all that surprising to me that they would need to focus all their attention right now on resolving the bricking issue even if it means ignoring emails. Perhaps they are trying to meet the deadline they set upon themselves, but I wouldn't count on it. This is the kind of thing that can cause major delays.