Device trees and armv5

[Yuri Honegger <yuri.honegger%icloud.com@localhost>]

Hello,
Recently, I've been playing around with porting NetBSD to the Lego Mindstorms EV3. 

The EV3 is based on an armv5 processor. I see that there are some ports that support armv5 and even the particular core used by the EV3. 

On linux, the EV3 support is done using device trees. While NetBSD also has device tree support, it seems to be limited to armv6 or higher.
Is there a technical reason for it, or is it mainly because there hasn't been any development effort to add armv5 support?

Also, what is the preferred way to add support for a new system: Fixing device trees so GENERIC also works with armv5, 
or adding a new set of kernel configuration files specific to the EV3 to arch/evbarm/conf?

Thank you