Currently RadChartView does not support StepLine series type. However It is in our plans to implement it and I cannot give you a specific timeframe when it will be supported.
Regarding your other question. What you have described sounds like a range series. If this is so, it is also in our future plans and it is not supported at that moment. As a workaround you could try using two stacked area series and set the color of the first one to be transparent.
Also, while it is true that we would encourage you to use our new RadChartView control for your new development, we would also like to note that currently you should do so based on the specific project requirements you have as the feature sets provided by both controls differ to some extent.
the Telerik team
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