It will be a nice addition for the chart to display harvey balls, where each ball is displayed exactly under one bar (or another data point representation).

If you have BarSeries with CombineMode set to "Stack" with zero values, the bars are placed to the maximum of the y-axis. 
As a work-around, you would need to manually adjust the Maximum value of the vertical axis.

Allow the user to customize the origin of rotation for axis labels.

DateTimeContinuousAxis displays incorrect labels when MajorStepUnit is Month. There are two labels for some months with 31 days.

This is visible only with longer labels, check the attached image.

Presently the trackball is displayed after a hold gesture. It will be a good addition to the features of the chart if the trackball can get displayed after a single tap.

Series labels are not displayed for horizontal BarSeries in UWP.

If the series is added after the page constructor, the vertical axis labels are not shown.

As a workaround, create the series in the constructor and set its ItemsSource at a later stage.

Bring the LabelRotationAngle property to Axes in Xamarin.Forms. 

See LabelRotationAngle here for reference: http://docs.telerik.com/devtools/wpf/controls/radchartview/axes/axis 

Bars are too thin in iOS when items are per day.

On iOS is whenever the first series  ItemSource has a null value, the other series are not plotted correctly in the graph. 

When having many stack bar series in one chart, some data points are rendered behind another data points. Check the attached image: how it looks on android and on iOS

Add support for range series. The series are available in the native charts
Android - RangeBarSeries 
iOS RangeBar and RangeColumn Series
UWP RangeBar, Range Series.

Please add these series to Chart for Xamarin.Forms. 

1. Change the view from BarSeries to Pie Series
     => Observe the PieChart loads as expected
2. Change the selection back to "Bar Series"
     => Observe BarSeries continues to operate as expected
3. Change the selection from "Bar Series" to "Pie Series"
     => Observe the following exception

Java.Lang.NullPointerException: 'Attempt to read from field 'double com.telerik.widget.chart.visualization.pieChart.PieUpdateContext.radius' on a null object reference'

Workaround: 
Remove the ShowLabels from Pie Series.

When setting LabelTextColor, it does not apply to the chart axis

verticalAxis.LabelTextColor = Android.Graphics.Color.Red;

horizontalAxis.LineColor = Android.Graphics.Color.Red;

If you add a View Annotation with an image to the iOS Chart through a custom renderer and the Chart has zoom and pan behavior applied, the annotation displays outside the axes when the Chart is zoomed.

For Chart with ScatterLineSeries, in case the ItemsSource contains points with following sample horizontal values: 0, 2, 4, 6, 8, 6, 4, 2, 0, ZoomBehavior does not work correctly on iOS  - when ZoomMode is set to "Both", the  points are taken in incorrect order and the result is a zig-zag chart.

Currently, depending on the platform, the first piece of the pie is drawn at 3 or 9 o'clock. It should be possible for the developer to set the starting point to be 12 o'clock.