Add detials on backwards compatibility and motivation

Signed-off-by: Philipp Stehle <philipp.stehle@sap.com>
Co-authored-by: Pavel Busko <pavel.busko@sap.com>
Co-authored-by: Scott Rigby <scott@r6by.com>

Author: 3 people

hips/hip-0016.md

@@ -81,6 +81,9 @@ Users of a parent chart instead have to provide values to the subcharts directly
 
 This HIP would allow to freely structure the values the user interacts with.
 
+The problem described above is less severe, if the subchart author, parent chart author and consumer are the same person or team.
+It becomes much more relevant for parent chart authors, that want to consume existing charts and provide it to a number of users without leaking the internal structure (i.e. the fact that it is using subcharts and how many) to the users.
+
 ## Rationale
 
 Using the same parent chart as in the [specification](#specification) without `export-value`, the `port` value must match and must be specified twice by the user.
@@ -98,7 +101,13 @@ The proposed structure is not only cleaner for the user, but also less error pro
 
 ## Backwards Compatibility
 
-This change won't break any existing Helm chart since it only adds new mechanisms.
+On one hand this change won't break any existing Helm chart since it only adds new mechanisms.
+On the other hand installing a chart which requires this feature with older versions of Helm make it fail silently, as values won't be passed to the child.
+There is currently no way to specify a minimum Helm version.
+The current workaround is to add this to a parent chart template, which will fix the otherwise silent failure:
+`{{- if semverCompare ">3.10.0" .Capabilities.HelmVersion.Version }} {{- fail "This chart requires helm version 3.10.0 or higher" }} {{- end }}`.
+A built-in mechanism to specify a minimum Helm version for a chart could be introduced in a separate HIP.
+Until such time, the introduction of this `export-values` functionality would require documenting this workaround for chart authors who wish to make their parent charts depend on the Helm version that introduced this functionality.
 
 ## Reference Implementation