Would it be possible to add the attribute also to layout updates?

[danielpoe]

Something like this would also be cool:

  <CHECKOUT_PROGRESSBAR  ifconfig="featureflag/v2">
        <reference name="content">
            <block type="aoe_statefulcheckout/parts_progress" name="aoe_statefulcheckout_progress"
                   template="aoe_statefulcheckout/parts/progress_v2.phtml"/>
        </reference>
    </CHECKOUT_PROGRESSBAR_1>

 <CHECKOUT_PROGRESSBAR ifconfig="featureflag/v1" >
        <reference name="content">
            <block type="aoe_statefulcheckout/parts_progress" name="aoe_statefulcheckout_progress"
                   template="aoe_statefulcheckout/parts/progress.phtml"/>
        </reference>
    </CHECKOUT_PROGRESSBAR>

Usage

 <aoe_statefulcheckout_emptycart>
        <update handle="CHECKOUT_PROGRESSBAR" />

is used