I offer my wholehearted support for this motion
I think the two databases could easily be synchronized, so that users can still contribute using Lokalize (or other .po editor) pulling/pushing messages directly to KDE servers.
Yes, the Translate extension export can handle that. When translation for MediaWiki started here, there were people still translating via direct commit, it wasn't an immediate complete switch.
Of course, it's easier for people to coordinate and collaborate if they use a single tool, so the general idea is to support only the languages whose teams want to use translatewiki.net, meaning that all of them want to move here and no conflicts happen.