No, because the cross platform tools will not work on WP7.8 because cross platform tool developers do not have native code support. App developers cannot use a cross platform tool to target WP7.8 because the cross-platform tool does not and cannot support WP7.8, the developer would have to rewrite apps for WP7.8 specifically. By "throwing away their current know how" they would be trying to save themselves time and money.